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Web Authoring FAQ
This document answers questions asked frequently by web authors. While
its focus is on HTML-related questions, this FAQ also answers some
questions related to CSS, HTTP, JavaScript, server configuration, etc.
This document is maintained by Darin McGrew <[email protected]> of
the Web Design Group, and is posted regularly to the newsgroup
comp.infosystems.www.authoring.html. It was last updated on October
20, 2001.
Index
1. Preamble
1. Copyright and Disclaimer
2. Where is the latest version of this document?
3. How can I contribute to this document?
4. Can I email the author my questions?
5. Credits
2. Other Documents
1. Where can I learn about the WWW?
2. Where can I learn about HTML?
3. Where can I find a list of all the current HTML tags?
4. Where can I learn about CSS?
5. Where can I learn about SGML?
6. Where can I learn about XML (XSL)?
7. Where can I learn about XHTML?
8. Where can I learn about SSI ("SHTML")?
9. Where can I learn about CGI?
10. Where can I learn about JavaScript (LiveScript, JScript,
EMCAScript, DOM)?
3. Getting Started
1. What is everyone using to write HTML?
2. How can I show HTML examples without them being interpreted as
part of my document?
3. How do I get special characters in my HTML?
4. Should I put quotes around attribute values?
5. How can I include comments in HTML?
6. How can I avoid using the whole URL?
7. Should I end my URLs with a slash?
8. How can I check for errors?
9. What is a DOCTYPE? Which one do I use?
4. Web Publishing
1. Where can I put my newly created Web pages?
2. How can I get my own domain name?
3. How can I block my hosting service's advertisements?
4. Where can I announce my site?
5. Is there a way to get indexed better by the search engines?
6. How do I prevent my site from being indexed by search engines?
7. How do I redirect someone to another page?
8. How do I password protect my web site?
9. How do I stop my page from being cached?
10. How do I hide my source?
11. How do I hide my URL?
12. How do I detect what browser is being used?
13. How do I get my visitors' email addresses?
14. Why is my custom 404 message not displayed?
5. Web Design
1. How do I include one file in another?
2. How do I run a program on my web page?
3. Which should I use, &entityname; or &#number; ?
4. Should I use lower case or upper case for tags?
5. For what screen size should I write?
6. Why does my page display fine in one browser but incorrectly
or not at all in another?
7. Why does the browser show my plain HTML source?
8. How do I freeze the URL displayed in a visitor's browser?
9. How do I put links along the left side of my page?
10. How can I specify colors?
11. How do I change the color of some text?
12. How can I specify my scrollbar colors?
13. How can I specify fonts in my Web pages?
6. Hyperlinks
1. How do I create a link?
2. How do I link to a location in the middle of an HTML document?
3. How do I create a link that opens a new window?
4. How do I create a link that opens a new window of a specific
size?
5. How do I create a button which acts like a link?
6. How do I create a back button on my page?
7. How do I create a button that automatically bookmarks my site?
8. How do I create a button that prints my page?
9. How do I create a link that sends me email?
10. How do I specify a subject for a mailto link?
11. How do I turn off underlining on my links?
12. How can I have two sets of links with different colors?
13. How can I make links change when the cursor is over them?
14. Why are my hyperlinks coming out all wrong or not loading?
15. Why does my link work in Internet Explorer but not in
Netscape?
7. Images
1. How can I display an image on my page?
2. Which image format should I use?
3. How do I link an image to something?
4. How can I create a thumbnail image that is linked to the
full-sized image?
5. How do I link different parts of an image to different things?
6. How do I eliminate the blue border around linked images?
7. Why am I getting a colored whisker to the left or right of my
image?
8. How do I eliminate the space around/between my images?
9. Why are my images coming out all wrong or not loading?
10. How do I make animated GIFs?
11. How can I display random images?
12. How do I prevent people from saving my images?
13. Can I put markup in ALT text?
14. How do I align an image to the right (or left)?
15. How can I specify background images?
16. How do I have a fixed background image?
17. How do I have a non-tiled background image?
8. Other Media
1. How do I let people download a file from my page?
2. Why did my link to a ... file download a bunch of characters
instead?
3. How do I force the browser to download a file? How do I force
the browser to show/play a file itself? How do I force a file
to be opened by a particular program?
4. How do I get an audio file to play automatically when someone
visits my site?
5. How can I strip all the HTML from a document to get plain
text?
9. Presentational Effects
1. How can I make a custom rule?
2. How can I make a list with custom bullets?
3. Where can I get a "hit counter"?
4. How do I display the current date or time in my document?
5. How do I get scrolling text in the status bar?
6. How do I right align or justify text?
7. How do I indent the first line in my paragraphs?
8. How do I indent a lot of text?
9. How do I eliminate the margins around my page?
10. How do I do a page break?
11. How can I have a custom icon when people bookmark my site?
10. HTML Tables
1. How do I make a table which looks good on non-supporting
browsers?
2. Can I nest tables within tables?
3. How can I use tables to structure forms?
4. How do I center a table?
5. How do I align a table to the right (or left)?
6. Can I use percentage values for <TD WIDTH=...>?
7. Why doesn't <TABLE WIDTH="100%"> use the full browser width?
8. Why is there extra space before or after my table?
9. Are there any problems with using tables for layout?
11. HTML Forms
1. How do I use forms?
2. How do I get form data emailed to me?
3. How can I use tables to structure forms?
4. How can I eliminate the extra space after a </form> tag?
5. How do I make a form so it can be submitted by hitting ENTER?
6. How do I set the focus to the first form field?
7. How can I make a form with custom buttons?
8. Can I have two or more Submit buttons in the same form?
9. Can I have two or more actions in the same form?
10. How can I require that fields be filled in, or filled in
correctly?
11. Can I prevent a form from being submitted again?
12. How can I allow file uploads to my web site?
13. How can I use forms for pull-down navigation menus?
12. HTML Frames
1. How do I create frames? What is a frameset?
2. How do I make a link or form in one frame update another
frame?
3. Why do my links open new windows rather than update an
existing frame?
4. How do I update two frames at once?
5. How do I get out of a frameset?
6. How do I make sure my framed documents are displayed inside
their frameset?
7. Is there a way to prevent getting framed?
8. How do I specify a specific combination of frames instead of
the default document?
9. How do I remove the border around frames?
10. How do I make a frame with a vertical scrollbar but without a
horizontal scrollbar?
11. How do I change the title of a framed document?
12. Why aren't my frames the exact size I specified?
13. Are there any problems with using frames?
14. Do search engines dislike frames?
Section 1: Preamble
1.1. Copyright and Disclaimer
Copyright ╘ 1996-2001 by the Web Design Group. This material may be
distributed only subject to the terms and conditions set forth in the
Open Publication License, v1.0 or later (the latest version is
presently available at http://www.opencontent.org/openpub/).
This information is offered in good faith and in the hope that it may
be useful, but it is not guaranteed to be correct, up to date, or
suitable for any particular purpose. The author accepts no liability
in respect of this information or its use.
1.2. Where is the latest version of this document?
The official home of this document on the Web is:
*<URL:http://www.htmlhelp.com/faq/html/> (index of HTML version)
*<URL:http://www.htmlhelp.com/faq/html/all.html> (single-file HTML
version)
*<URL:http://www.htmlhelp.com/faq/html/all.txt> (single-file text
version)
A Dutch translation of this document is available at:
*<URL:http://www.htmlhelp.com/nl/faq/html/>
A French translation of this document is available at:
*<URL:http://www.htmlhelp.com/fr/faq/html/>
NOTE: If you want to mirror the FAQ on your WWW site on a
publicly-visible server, please make sure you keep it up-to-date.
Other known sources are:
*The text version is posted to the newsgroups
*news:comp.infosystems.www.authoring.html
*news:comp.answers
*news:news.answers
*RTFM and mirror sites:
*ftp://rtfm.mit.edu/pub/usenet/news.answers/www/authoring-faq
*http://www.cs.ruu.nl/cgi-bin/faqwais (Europe)
*http://www.cis.ohio-state.edu/hypertext/faq/usenet/ (USA)
*Or send email to mailto:[email protected] with
send usenet/news.answers/www/authoring-faq
in the body of your message
1.3. How can I contribute to this document?
If you would like to contribute to this FAQ, please send mail to
<[email protected]>. All contributors will be listed in the credits.
1.4. Can I email the author my questions?
Please do not ask me questions via email. Please post questions to an
appropriate public forum, where they will be read (and possibly
answered/discussed) by many people with more expertise than me. Think
carefully before posting; you'll get more useful answers if you post
clear, complete questions.
If you think something already in the FAQ needs clarifying, or if you
would like to offer a concise, well-written answer to a frequently
asked question that is not yet in the FAQ, then feel free to send me
email.
1.5. Credits
All information contained in this FAQ was originally compiled by
members of the Web Design Group, principally Arnoud "Galactus"
Engelfriet, John Pozadzides, and Darin McGrew. The Dutch translation
of this FAQ was prepared by Rijk van Geijtenbeek. The French
translation of this FAQ was prepared by CИdrik Rousseau.
Additional input has been provided by Boris Ammerlaan, Martin Atkins,
Lori Atwater, Alex Bell, Robert Breeser, Stan Brown, Roger Carbol,
Alex Chapman, Jan Roland Eriksson, Jon Erlandson, Mark Evans, Peter
Evans, Joe Faulds, Alan Flavell, Rijk van Geijtenbeek, Lucie Gelinas,
Bjoern Hoehrmann, Tina Marie Holmboe, Cliff Howard, Thomas Jespersen,
Peter Jones, Nick Kew, Jukka Korpela, Simon Lee, Nick Lilavois, Kelly
Martin, Neal McBurnett, Glen McDonald, Dan McGarry, Ken O'Brien,
Timothy Prodin, Steve Pugh, Liam Quinn, Colin Reynolds, Kai SchДtzl,
Randal L. Schwartz, Doug Sheppard, Sue Sims, Toby Speight, Warren
Steel, Ian Storms, Peter Thomson, Daniel Tobias, Diane Wilson, and no
doubt others I've forgotten to credit.
Thanks everyone! Your comments, criticisms, and suggestions have
considerably improved this FAQ.
Section 2: Other Documents
2.1. Where can I learn about the WWW?
The World Wide Web is "the universe of network-accessible information
(available through your computer, phone, television, or networked
refrigerator...)." The World Wide Web began as a networked information
project at CERN.
*A Little History of the World Wide Web
<URL:http://www.w3.org/History.html>
*About the World Wide Web <URL:http://www.w3.org/WWW/>
*W3C in 7 Points <URL:http://www.w3.org/Consortium/Points/>
2.2. Where can I learn about HTML?
HyperText Markup Language is a simple markup language used to create
platform-independent hypertext documents on the World Wide Web. Most
hypertext documents on the web are written in HTML.
*W3C's HTML 4.01 Recommendation <URL:http://www.w3.org/TR/html4/>
*WDG's HTML 4.0 Reference
<URL:http://www.htmlhelp.com/reference/html40/>
*Jukka Korpela's "Getting Started with HTML"
<URL:http://www.cs.tut.fi/~jkorpela/html-primer.html>
2.3. Where can I find a list of all the current HTML tags?
The current recommendation is XHTML 1.0, which is a reformulation of
HTML 4.01 as an XML 1.0 application. HTML 4.01 is an update with minor
corrections to HTML 4.0. HTML 4 extends HTML 3.2 to include support
for frames, internationalization, style sheets, advanced tables, and
more. The new markup introduced by HTML 4 is not well supported by
current browsers, but much of it can be used safely in non-supporting
browsers.
HTML 4
*http://www.w3.org/TR/html4/ -- the official HTML 4.01 Recommendation
*http://www.htmlhelp.com/reference/html40/ -- a handy HTML 4.0
reference, with notes on using poorly supported features safely
HTML 3.2
*http://www.w3.org/TR/REC-html32 -- the official HTML 3.2
Recommendation
*http://www.htmlhelp.com/reference/wilbur/ -- a more readable version
of the above
*http://www.cs.tut.fi/~jkorpela/HTML3.2/ -- Jukka Korpela's "Learning
HTML 3.2 by Examples"
Browser-Specific Markup
*http://www.blooberry.com/indexdot/html/supportkey/a.htm -- Brian
Wilson's checklist of browser support for HTML tags and attributes
*http://developer.netscape.com/docs/manuals/htmlguid/index.htm -- a
list of Netscape HTML tags (early 1998)
*http://msdn.microsoft.com/workshop/author/html/reference/elements.asp#ie40_html
-- a list of Microsoft HTML tags
2.4. Where can I learn about CSS?
Cascading Style Sheets are a standards-based mechanism for suggesting
presentational style (e.g., fonts, colors, layout) for HTML documents.
CSS is flexible and cross-platform, and is designed to preserve the
accessibility of the document's structural content (even when all or
part of the author's style sheet is ignored). A single style sheet can
be used by multiple documents to suggest a common cohesive style,
which is more efficient than using repetitive presentational markup in
each individual document.
*W3C's CSS Level 2 Recommendation <URL:http://www.w3.org/TR/REC-CSS2/>
*WDG's Guide to Cascading Style Sheets
<URL:http://www.htmlhelp.com/reference/css/>
*The CSS Pointers Group <URL:http://css.nu/>
*The HTML Writers Guild's CSS FAQ
<URL:http://www.hwg.org/resources/faqs/cssFAQ.html>
2.5. Where can I learn about SGML?
Standard Generalized Markup Language is a language used to define the
syntax of markup languages. HTML is an SGML application (a markup
language defined in SGML).
*W3C's "On SGML and HTML"
<URL:http://www.w3.org/TR/html401/intro/sgmltut.html>
*A Tutorial Introduction to SGML Architectures
<URL:http://www.isogen.com/papers/archintro.html>
2.6. Where can I learn about XML (XSL)?
Extensible Markup Language is another language used to define the
syntax of markup languages. XML is a subset of SGML, and is designed
to represent arbitrary structured data in a text format. XSL is a
stylesheet language for styling XML documents.
*W3C's XML 1.0 Recommendation <URL:http://www.w3.org/TR/REC-xml>
*W3C's "XML in 10 Points"
<URL:http://www.w3.org/XML/1999/XML-in-10-points.html>
*W3C's XSL Specification <URL:http://www.w3.org/Style/XSL/>
2.7. Where can I learn about XHTML?
Extensible HyperText Markup Language is a reformulation of HTML as an
XML application. Because it is an XML application, the syntax
requirements of XHTML are more restrictive than those of HTML.
Otherwise, XHTML 1.0 mirrors the functionality of HTML 4.01.
*W3C's XHTML 1.0 Recommendation <URL:http://www.w3.org/TR/xhtml1/>
2.8. Where can I learn about SSI ("SHTML")?
Server-Side Includes allow various directives (e.g., to include the
content of another file) to be embedded within web documents. The web
server processes SSI directives each time a document that uses SSI is
retreived. Documents that use SSI are often identified with a .shtml
filename extension, but there is no "SHTML" language as such.
Implementation details vary among web servers; consult your server
documentation for details.
* SSI Tutorial for the Apache server
<URL:http://httpd.apache.org/docs/howto/ssi.html>
* SSI Documentation for the Apache server
<URL:http://httpd.apache.org/docs/mod/mod_include.html>
2.9. Where can I learn about CGI?
Common Gateway Interface is a standard interface between external
programs and web servers. Unlike static HTML documents, CGI programs
can produce dynamic information based on form data submitted by the
user, on information in a database, or on any other data available to
the program.
* WDG's CGI Programming FAQ
<URL:http://www.htmlhelp.com/faq/cgifaq.html>.
* CGI Tutorial for the Apache server
<URL:http://httpd.apache.org/docs/howto/cgi.html>
2.10. Where can I learn about JavaScript (LiveScript, JScript,
EMCAScript, DOM)?
JavaScript is a cross-platform, interpretted, object-oriented
language originally designed for client-side web scripting. The
elements of web pages can be manipulated via JavaScript as objects
specified by the Document Object Model (DOM). This enables dynamic
effects like image roll-overs and interactive effects like pages that
change in response to user input without being reloaded from the
server.
LiveScript was Netscape's initial pre-release name for JavaScript.
JScript is Microsoft's implementation of the language. ECMAScript is
a standardized version based upon Netscape's JavaScript and
Microsoft's JScript.
* ECMA Standard ECMA-262 (ECMAScript Language Specification)
<URL:http://www.ecma.ch/ecma1/stand/ecma-262.htm>
* W3C's Document Object Model, level 2 (DOM2)
<URL:http://www.w3.org/TR/WD-DOM-Level-2/>
* W3C's Document Object Model, level 1 (DOM1)
<URL:http://www.w3.org/TR/REC-DOM-Level-1/>
* Netscape's JavaScript Developer Central (DevEdge Online)
<URL:http://developer.netscape.com/tech/javascript/>
* Microsoft's Scripting Technologies: JScript
<URL:http://msdn.microsoft.com/scripting/jscript/>
* WDG's advice on JavaScript and accessibility
<URL:http://valet.htmlhelp.com/page/js.html>
Section 3: Getting Started
3.1. What is everyone using to write HTML?
It seems that everyone has a different preference for which tool
works best for them. You may find lists of HTML authoring tools at:
* http://dir.yahoo.com/Computers_and_Internet/Software/Internet/World_Wide_Web/HTML_Editors/
* http://www.winfiles.com/ (search "HTML Editors")
* http://www.tucows.com/ (Win 95, Win 3.x, Macintosh, OS/2)
* http://shareware.cnet.com/ (search "HTML editor")
Keep in mind that typically the less HTML the tool requires you to
know, the worse the output of the HTML. In other words, you can
always do it better by hand if you take the time to learn a little
HTML.
3.2. How can I show HTML examples without them being interpreted as part
of my document?
Within the HTML example, first replace the "&" character with "&"
everywhere it occurs. Then replace the "<" character with "<" and
the ">" character with ">" in the same way.
The next Q&A addresses the more general issue of representing
arbitrary characters in HTML documents.
3.3. How do I get special characters in my HTML?
The answer to the previous question addressed the special case of
the less-than ('<'), greater-than ('>'), and ampersand ('&')
characters. In general, the safest way to write HTML is in US-ASCII
(ANSI X3.4, a 7-bit code), expressing characters from the upper half
of the 8-bit code by using HTML entities. See the answer to "Which
should I use, &entityname; or &#number; ?"
Working with 8-bit characters can also be successful in many
practical situations: Unix and MS-Windows (using Latin-1), and also
Macs (with some reservations).
The available characters are those in ISO-8859-1, listed at
<URL:http://www.htmlhelp.com/reference/charset/>. ISO-8859-1 is
intended for English, French, German, Spanish, Portuguese, and
various other western European languages. (It is inadequate for many
languages of central and eastern Europe and elsewhere, let alone for
languages not written in the Roman alphabet.) On the Web, these are
the only characters reliably supported. In particular, characters
128 through 159 as used in MS-Windows are not part of the ISO-8859-1
code set and will not be displayed as Windows users expect. These
characters include the em dash, en dash, curly quotes, bullet, and
trademark symbol; neither the actual character (the single byte) nor
its &#nnn; decimal equivalent is correct in HTML. Also, ISO-8859-1
does not include the Euro currency character. (See the last
paragraph of this answer for more about such characters.)
On platforms whose own character code isn't ISO-8859-1, such as
MS-DOS and Mac OS, there may be problems: you have to use text
transfer methods that convert between the platform's own code and
ISO-8859-1 (e.g., Fetch for the Mac), or convert separately (e.g.,
GNU recode). Using 7-bit ASCII with entities avoids those problems,
but this FAQ is too small to cover other possibilities in detail.
Mac users - see the notes at
<URL:http://www.htmlhelp.com/reference/charset/>.
If you run a web server (httpd) on a platform whose own character
code isn't ISO-8859-1, such as a Mac or an IBM mainframe, then it's
the job of the server to convert text documents into ISO-8859-1 code
when sending them to the network.
If you want to use characters not in ISO-8859-1, you must use HTML 4
or XHTML rather than HTML 3.2, choose an appropriate alternative
character set (and for certain character sets, choose the encoding
system too), and use one method or other of specifying this. See the
HTML 4.01 Recommendation at <URL:http://www.w3.org/TR/html4/> and
the Babel site at <URL:http://babel.alis.com:8080/> for more
details. Another useful resource for internationalization issues is
at <URL:http://ppewww.ph.gla.ac.uk/%7Eflavell/charset/>.
3.4. Should I put quotes around attribute values?
It is never wrong to quote attribute values, and many people
recommend quoting all attribute values even when the quotation marks
are technically optional. XHTML 1.0 requires all attribute values to
be quoted. Like previous HTML specifications, HTML 4 allows
attribute values to remain unquoted in many circumstances (e.g.,
when the value contains only letters and digits). See
<URL:http://www.w3.org/TR/html4/intro/sgmltut.html#attributes> for
the exact rules.
Be careful when your attribute value includes double quotes, for
instance when you want ALT text like "the "King of Comedy" takes a
bow" for an image. Humans can parse that to know where the quoted
material ends, but browsers can't. You have to code the attribute
value specially so that the first interior quote doesn't terminate
the value prematurely. There are two main techniques:
* Escape any quotes inside the value with " so you don't terminate
the value prematurely: ALT="the "King of Comedy" takes a
bow". (" is not part of the formal HTML 3.2 spec, though most
current browsers support it.)
* Use single quotes to enclose the attribute value: ALT='the "King of
Comedy" takes a bow'.
Both these methods are correct according to the spec and are
supported by current browsers, but both were poorly supported in
some earlier browsers. The only truly safe advice is to rewrite the
text so that the attribute value need not contain quotes, or to
change the interior double quotes to single quotes, like this:
ALT="the 'King of Comedy' takes a bow".
3.5. How can I include comments in HTML?
A comment declaration starts with "<!", followed by zero or more
comments, followed by ">". A comment starts and ends with "--", and
does not contain any occurrence of "--" between the beginning and
ending pairs. This means that the following are all legal HTML
comments:
* <!-- Hello -->
* <!-- Hello -- -- Hello-->
* <!---->
* <!------ Hello -->
* <!>
But some browsers do not support the full syntax, so we recommend
you follow this simple rule to compose valid and accepted comments:
An HTML comment begins with "<!--", ends with "-->", and does
not contain "--" or ">" anywhere in the comment. Do not put
comments inside tags (i.e., between "<" and ">") in HTML
markup.
See <URL:http://www.htmlhelp.com/reference/wilbur/misc/comment.html>
for a more complete discussion.
3.6. How can I avoid using the whole URL?
The URL structure defines a hierarchy similar to a filesystem's
hierarchy of subdirectories or folders. The segments of a URL are
separated by slash characters ("/"). When navigating the URL
hierarchy, the final segment of the URL (i.e., everything after the
final slash) is similar to a file in a filesystem. The other
segments of the URL are similar to the subdirectories and folders in
a filesystem.
A relative URL omits some of the information needed to locate the
referenced document. The omitted information is assumed to be the
same as for the base document that contains the relative URL. This
reduces the length of the URLs needed to refer to related documents,
and allows document trees to be accessed via multiple access schemes
(e.g., "file", "http", and "ftp") or to be moved without changing
any of the embedded URLs in those documents.
Before the browser can use a relative URL, it must resolve the
relative URL to produce an absolute URL. If the relative URL begins
with a double slash (e.g., //www.htmlhelp.com/faq/html/), then it
will inherit only the base URL's scheme. If the relative URL begins
with a single slash (e.g., /faq/html/), then it will inherit the
base URL's scheme and network location.
If the relative URL does not begin with a slash (e.g., all.html ,
./all.html or ../html/), then it has a relative path and is resolved
as follows.
1. The browser strips everything after the last slash in the base
document's URL and appends the relative URL to the result.
2. Each "." segment is deleted (e.g., ./all.html is the same as
all.html, and ./ refers to the current "directory" level in the URL
hierarchy).
3. Each ".." segment moves up one level in the URL hierarchy; the ".."
segment is removed, along with the segment that precedes it (e.g.,
foo/../all.html is the same as all.html, and ../ refers to the
parent "directory" level in the URL hierarchy).
Some examples may help make this clear. If the base document is
<URL:http://www.htmlhelp.com/faq/html/basics.html>, then
all.html and ./all.html
refer to <URL:http://www.htmlhelp.com/faq/html/all.html>
./
refers to <URL:http://www.htmlhelp.com/faq/html/>
../
refers to <URL:http://www.htmlhelp.com/faq/>
../cgifaq.html
refers to <URL:http://www.htmlhelp.com/faq/cgifaq.html>
../../reference/
refers to <URL:http://www.htmlhelp.com/reference/>
Please note that the browser resolves relative URLs, not the server.
The server sees only the resulting absolute URL. Also, relative URLs
navigate the URL hierarchy. The relationship (if any) between the
URL hierarchy and the server's filesystem hierarchy is irrelevant.
For a full discussion of the proper form of URLs, see
<URL:http://www.w3.org/Addressing/>.
3.7. Should I end my URLs with a slash?
The URL structure defines a hierarchy similar to a filesystem's
hierarchy of subdirectories or folders. The segments of a URL are
separated by slash characters ("/"). When navigating the URL
hierarchy, the final segment of the URL (i.e., everything after the
final slash) is similar to a file in a filesystem. The other
segments of the URL are similar to the subdirectories and folders in
a filesystem.
When resolving relative URLs (see the answer to the previous
question), the browser's first step is to strip everything after the
last slash in the URL of the current document. If the current
document's URL ends with a slash, then the final segment (the
"file") of the URL is null. If you remove the final slash, then the
final segment of the URL is no longer null; it is whatever follows
the final remaining slash in the URL. Removing the slash changes the
URL; the modified URL refers to a different document and relative
URLs will resolve differently.
For example, the final segment of the URL
http://www.htmlhelp.com/faq/html/ is empty; there is nothing after
the final slash. In this document, the relative URL all.html
resolves to http://www.htmlhelp.com/faq/html/all.html (an existing
document). If the final slash is omitted, then the final segment of
the modified URL http://www.htmlhelp.com/faq/html is "html". In
this (nonexistent) document, the relative URL all.html would resolve
to http://www.htmlhelp.com/faq/all.html (another nonexistent
document).
When they receive a request that is missing its final slash, web
servers cannot ignore the missing slash and just send the document
anyway. Doing so would break any relative URLs in the document.
Normally, servers are configured to send a redirection message when
they receive such a request. In response to the redirection message,
the browser requests the correct URL, and then the server sends the
requested document. (By the way, the browser does not and cannot
correct the URL on its own; only the server can determine whether
the URL is missing its final slash.)
This error-correction process means that URLs without their final
slash will still work. However, this process wastes time and network
resources. If you include the final slash when it is appropriate,
then browsers won't need to send a second request to the server.
The exception is when you refer to a URL with just a hostname (e.g.,
http://www.htmlhelp.com). In this case, the browser will assume that
you want the main index ("/") from the server, and you do not have
to include the final slash. However, many regard it as good style to
include it anyway.
For a full discussion of the proper form of URLs, see
<URL:http://www.w3.org/Addressing/>.
3.8. How can I check for errors?
Various software is available to find errors in your web documents
automatically. HTML validators are programs that check HTML
documents against a formal definition of HTML syntax and then output
a list of errors. Validation is important to give the best chance of
correctness on unknown browsers (both existing browsers that you
haven't seen and future browsers that haven't been written yet).
HTML linters (checkers) are also useful. These programs check
documents for specific portability problems, including some caused
by invalid markup and others caused by common browser bugs. Linters
may pass some invalid documents, and they may fail some valid ones.
All validators are functionally equivalent; while they may have
different reporting styles, they will find the same errors given
identical input. Different linters are programmed to look for
different problems, so their reports will vary significantly from
each other. Also, some programs that are called validators (e.g. the
"CSE HTML Validator") are really linters/checkers. They are still
useful, but they should not be confused with real HTML validators.
When checking a site for errors for the first time, it is often
useful to identify common problems that occur repeatedly in your
markup. Fix these problems everywhere they occur (with an automated
process if possible), and then go back to identify and fix the
remaining problems.
While checking for errors in the HTML, it is also a good idea to
check for hypertext links which are no longer valid. There are
several link checkers available for various platforms which will
follow all links on a site and return a list of the ones which are
non-functioning.
You can find a list of validators, linters, and link checkers at
<URL:http://www.htmlhelp.com/links/validators.htm>. Especially
recommended is the use of an SGML-based validator such as the WDG
HTML Validator <URL:http://www.htmlhelp.com/tools/validator/> or
W3C HTML Validation Service <URL:http://validator.w3.org/>.
3.9. What is a DOCTYPE? Which one do I use?
According to HTML standards, each HTML document begins with a
DOCTYPE declaration that specifies which version of HTML the
document uses. The DOCTYPE declaration is useful primarily to
SGML-based tools like HTML validators, which must know which version
of HTML to use in checking the document's syntax. Browsers generally
ignore DOCTYPE declarations.
See <URL:http://www.htmlhelp.com/tools/validator/doctype.html> for
information on choosing an appropriate DOCTYPE declaration.
Note that the public identifier section of the DOCTYPE declaration
is case sensitive. Some versions of Netscape Composer are known to
insert the lower-case "-//w3c//dtd html 4.0 transitional//en",
rather than the correct mixed-case "-//W3C//DTD HTML 4.0
Transitional//EN".
Section 4: Web Publishing
4.1. Where can I put my newly created Web pages?
Many ISPs offer web space to their dial-up customers. Typically this
will be less than 5MB, and there may be other restrictions; for
example, many do not allow commercial use of this space.
There are several companies and individuals who offer free web
space. This usually ranges from 100KB up to 1MB, and again there are
often limitations on its use. They may also require a link to their
home page from your pages. For pointers to providers of free web
space, see <URL:http://www.freewebspace.net/>.
There are also many web space providers (aka presence providers) who
will sell you space on their servers. Prices will range from as
little as $1 per month, up to $100 per month or more, depending upon
your needs. Non-virtual Web space is typically the cheapest,
offering a URL like: http://www.some-provider.com/yourname/ For a
little more, plus the cost of registering a domain name, you can get
virtual web space, which will allow you to have a URL like
http://www.yourname.com/.
If you have some permanent connection to the Internet, perhaps via
leased line from your ISP then you could install an httpd and
operate your own Web server. There are several Web servers available
for almost all platforms.
If you just wish to share information with other local users, or
people on a LAN or WAN, you could just place your HTML files on the
LAN for everyone to access, or alternatively if your LAN supports
TCP/IP then install a Web server on your computer.
4.2. How can I get my own domain name?
The Internet Corporation for Assigned Names and Numbers (ICANN)
maintains a list of accredited registrars at
<URL:http://www.icann.org/registrars/accredited-list.html>. Any of
the companies on this list can register a domain name for you.
4.3. How can I block my hosting service's advertisements?
Check the Terms of Service (TOS) agreement for your hosting service.
It almost certainly prohibits interfering with the advertisements
they add to your web pages. If you use some trick to block their
advertisements on your own, then your hosting service may delete
your account for violating its TOS.
However, there may be other options. Some hosting services will
remove the advertisements if you pay a small monthly fee. Others
will remove their default pop-up advertisements if you add static
banners yourself.
4.4. Where can I announce my site?
* comp.infosystems.www.announce -- a moderated newsgroup specifically
geared toward this subject. You need to obtain its FAQ list before
posting to it.
* http://www.submit-it.com/ lets you submit site information to 10
different major index sites for free. If you wish to pay you may
submit your site to more than 400 sites.
* http://ep.com/faq/webannounce.html is the How to Announce your New
Web Site FAQ.
4.5. Is there a way to get indexed better by the search engines?
There is no single technique, but a number of factors can help.
* Search engines index the textual content of your site, so use a
meaningful <TITLE>, use meaningful headings (<H1>, <H2>, and so on),
and provide meaningful ALT text for images.
* Many search engines ignore frames, so avoid them, and be sure to
provide useful NOFRAMES content if you do use them.
* Most search engines ignore image maps, forms, and JavaScript, so
make sure that navigating your site doesn't depend on them. Provide
normal links for site navigation.
* Avoid using META refresh, because many search engines penalize sites
that use it (META refresh has been used to trick search engines).
* The indexing programs of some search engines (including AltaVista
and Infoseek) will also take into account <META NAME="keywords"
CONTENT="..."> tags that appear in the <HEAD> part of your
documents. However, META keywords have been used to trick search
engines, so many will ignore your keywords list if you repeat a
given keyword too often. At this writing, "too often" means "more
than 7 times" to some popular engines, but that may change in the
future as indexing programs are changed to defend against trickery.
* If you include a <META NAME="description" CONTENT="..."> tag in the
<HEAD> part of your documents, then some search engines will use the
content of this tag as your site's description when displaying
search results. This won't affect your ranking in searches, but it
can help search engine users understand what your site offers when a
search does find your site.
The CONTENT attribute of the META keywords and description tags may
contain up to 1022 characters, but no markup other than entities.
You might want to preview your site with a text-only browser like
Lynx, to get an idea of how your site appears to search engines.
Search Engine Watch at <URL:http://searchenginewatch.com/> is a Web
site dedicated to search engines and strategies for Web page
authors.
Finally, note that some search engines ignore sites hosted by
well-known free hosting services. Other search engines index only a
certain number of documents per server, so while early customers of
free hosting services may be indexed, later customers may be
ignored.
4.6. How do I prevent my site from being indexed by search engines?
See
<URL:http://www.robotstxt.org/wc/exclusion.html>.
4.7. How do I redirect someone to another page?
The most reliable way is to configure the server to send out a
redirection instruction when the old URL is requested. Then the
browser will automatically get the new URL. This is the fastest and
most efficient way, and is the only way described here that can
convince indexing robots to phase out the old URL. For configuration
details consult your server admin or documentation (with NCSA or
Apache servers, use a Redirect statement in .htaccess).
If you can't set up a redirect, there are other possibilities. These
are inferior because they tell the search engines that there's still
a page at the old location, not that the page has moved to a new
location. But if it's impossible for you to configure redirection at
your server, here are two alternatives:
* Put up a small page with text like "This page has moved to
http://new.url/ -- please adjust your bookmarks."
* A Netscape and MSIE solution, which doesn't work on many other
browsers (and screws up the "back" button in Netscape) is:
<META HTTP-EQUIV="Refresh" CONTENT="x; URL=new.URL">
which will load the new URL after x seconds. This should go in the
HEAD of the document. But if you do this, also include a short text
saying "Document moved to new URL so-and-so" for other browsers.
(The screwing-up bit refers to the fact that if you press "Back"
after you have been redirected, you will be taken to the document
with the META refresh. Then the refresh will be activated, and so
you'll jump to the page you just tried to leave.)
4.8. How do I password protect my web site?
Password protection is done through HTTP authentication. The
configuration details vary from server to server, so you should read
the authentication section of your server documentation. Contact
your server administrator if you need help with this.
For example, if your server is Apache, see
<URL:http://httpd.apache.org/docs/misc/FAQ.html#user-authentication>.
JavaScript password scripts provide only a facade of security. At a
fundamental level, they work in one of two ways. Some scripts
convert the password into a URL, which keeps the document secret by
limiting the number of people who know its URL. Some scripts check
the password and then go to a specific URL, which protects the
document only from those who don't view the JavaScript source to get
the URL of the document. Neither mechanism is really secure.
4.9. How do I stop my page from being cached?
Browsers cache web documents; they store local copies of documents
to speed up repeated references to documents that haven't changed.
Also, many browsers are configured to use public proxy caches, which
serve many users (e.g., all customers of an ISP, or all employees
behind a corporate firewall). To effectively control how your
documents are cached you must configure your server to send
appropriate HTTP headers.
The Expires header is understood by virtually all caches. The cached
document will be retrieved again automatically once it has expired.
The Expires header must contain an HTTP date, which must be
Greenwich Mean Time (GMT), not local time.
HTTP 1.1 introduced the Cache-Control header, which provides more
flexibility for telling caches how to handle the document. For more
information, see the HTTP 1.1 draft (see
<URL:http://www.w3.org/Protocols/>).
The configuration details vary from server to server, so check your
server documentation. For example, if your server is Apache, see
<URL:http://httpd.apache.org/docs/mod/mod_expires.html> for
information about setting the Expires header, and
<URL:http://httpd.apache.org/docs/mod/mod_headers.html> for
information about setting other headers.
The Pragma header is generally ineffective because its meaning is
not standardized and few caches honor it. Using <META
HTTP-EQUIV=...> elements in HTML documents is also generally
ineffective; some browsers may honor such markup, but other caches
ignore it completely.
Further discussion can be found at
<URL:http://www.mnot.net/cache_docs/>.
4.10. How do I hide my source?
You can't. The HTML source is necessary for the browser to display
your document; you must send the complete, unencrypted source to the
browser. Even if a particular browser doesn't have a "View Source"
feature, there are many that do, and someone can always retrieve the
document by hand (using telnet) or from the browser's cache.
There are tricks that make it more difficult for some readers to
view or save your source (e.g., tricking newbies into thinking
there's nothing there by adding dozens of blank lines to the
beginning of the document, or using JavaScript to trap right-button
mouse events). However, just as with tricks that try to protect
images from being saved, these tricks have very limited
effectiveness and can cause various problems for law-abiding users.
4.11. How do I hide my URL?
You can't. URLs are fundamental to navigation on the WWW. The URL is
necessary for the browser to be able to retrieve your document. It
is impossible to hide the URL of a resource from the browser.
With that said, it is possible to somewhat obscure URLs via a
misfeature of frames. See the answer to "How do I freeze the URL
displayed in a visitor's browser?"
4.12. How do I detect what browser is being used?
Many browsers identify themselves when they request a document. A
CGI script will have this information available in the
HTTP_USER_AGENT environment variable, and it can use that to send
out a version of the document which is optimized for that browser.
Keep in mind not all browsers identify themselves correctly.
Microsoft Internet Explorer, for example, claims to be "Mozilla" to
get at Netscape enhanced documents.
And of course, if a cache proxy keeps the Netscape enhanced
document, someone with another browser will also get this document
if he goes through the cache.
For these reasons and others, it is not a good idea to play the
browser guessing game.
4.13. How do I get my visitors' email addresses?
You can't. Although each request for a document is usually logged
with the name or address of the remote host, the actual username is
almost never logged as well. This is mostly because of performance
reasons, as it would require that the server uses the ident protocol
to see who is on the other end. This takes time. And if a cache
proxy is doing the request, you don't get anything sensible.
But just stop to think for a minute... would you really want every
single site you visit to know your email address? Imagine the loads
of automated thank you's you would be receiving. If you visited 20
sites, you would get at least 20 emails that day, plus no doubt they
would send you invitations to return later. It would be a nightmare
as well as an invasion of privacy!
In Netscape 2.0, it was possible to automatically submit a form with
a mailto as action, using JavaScript. This would send email to the
document's owner, with the address the visitor configured in the
From line. Of course, that can be "[email protected]". This
was fixed by Netscape 2.01.
The most reliable way is to put up a form, asking the visitor to
fill in his email address. To increase the chances that visitors
will actually do it, offer them something useful in return.
4.14. Why is my custom 404 message not displayed?
If no browser displays your custom 404 messages, then your server
probably is not configured properly.
If only Internet Explorer ignores your custom 404 messages, then
you've been caught by its "friendly" HTTP error messages. When a
special HTTP response (e.g., a 404 response) is shorter than 512
bytes, Internet Explorer substitutes its own message for the one
delivered by the server. As a user of Internet Explorer, you can
disable this feature in the "Advanced" options panel. As a web
author, your only recourse is to make the error page longer.
Section 5: Web Design
5.1. How do I include one file in another?
HTML itself offers no way to seamlessly incorporate the content of
one file into another.
True dynamic inclusion of one HTML document (even in a different
"charset") into another is offered by the OBJECT element, but due to
shortcomings of browser versions in current use, it seems unwise to
rely on this yet for essential content. The same can be said for
IFRAME.
Two popular ways of including the contents of one file seamlessly
into another for the WWW are preprocessing and server-side
inclusion. A preprocessor converts its source into a plain HTML
document that you publish on your server. In contrast, documents
that use server-side inclusion are processed every time the document
is retrieved from the server.
Preprocessing techniques include the C preprocessor and other
generic text manipulation methods, and several HTML-specific
processors. There is a nice annotated list of HTML preprocessors at
<http://www.idocs.com/wmr/software/html+preprocessors/>.
Beware of making your "source code" non-portable. Also, the HTML can
only be validated after preprocessing, so the typical cycle "Edit,
Check, Upload" becomes "Edit, Preprocess, Check, Upload" (here,
"Check" includes whatever steps you use to preview your pages:
validation, linting, management walk-through etc.; and "upload"
means whatever you do to finally publish your new pages to the web
server).
A much more powerful and versatile preprocessing technique is to use
an SGML processor (such as the SP package) to generate your HTML;
this can be self-validating.
Examples of server-side inclusion are Server Side Includes (SSI,
supported by Apache, NCSA, and other web servers), and Microsoft's
Active Server Pages (ASP, supported by MS IIS). Processing occurs at
the time the documents are actually retrieved. A typical inclusion
looks like
<!--#include virtual="/urlpath/to/myfile.htm" -->
However, be sure to consult your own server's documentation, as the
details vary somewhat between implementations. The whole directive
gets replaced by the contents of the specified file.
Using server-side inclusion (a potentially powerful tool) merely as
a way to insert static files such as standard header/footers has
implications for perceived access speed and for server load, and is
better avoided on heavily loaded servers. If you use it in this way,
consider making the result cacheable (e.g., via "XBitHack full" on
Apache; setting properties of the "Response" object in ASP). Details
are beyond the scope of this FAQ but you may find this useful:
http://www.mnot.net/cache_docs/
Proper HTML validation of server-side inclusion is only possible
after server-side processing is done (e.g. by using an on-line
validator that retrieves the document from the server).
Another approach is to create a database-backed site, as described
in "Philip and Alex's Guide to Web Publishing" at
<URL:http://www.arsdigita.com/books/panda/>. A simple change to the
database template instantly changes the whole site.
Finally, note that if the included file contains arbitrary plain
text, then some provision must be made to convert the characters "&"
and "<" (in the plain text file) to the entities "&" and "<"
(in the HTML document).
5.2. How do I run a program on my web page?
Browsers don't allow web authors to download and run arbitrary
programs on the client system, because that would be an unacceptable
security risk. Users would be unable to visit untrusted web sites
safely.
You can link to an executable program file, allowing users to
download it. Users could then choose to run the program, assuming
that it runs on their operating systems, and that they are not
concerned about software viruses.
If you want to run the program on your web server, then check your
server documentation for configuration details for server-side
programs. General information is available in the CGI Programming
FAQ: http://www.htmlhelp.com/faq/cgifaq.html
When client-side scripting (e.g., JavaScript) is enabled on the
client system (browser), it can be used to perform computations and
to manipulate the data on and appearance of a web page.
If you want to launch a specialized viewer for a particular kind of
file, say Adobe Acrobat Reader when the visitor follows a link to a
PDF file, then that should be handled automatically by the visitor's
browser, assuming that it is configured correctly. You need only
configure your server to send the file with the correct MIME type.
5.3. Which should I use, &entityname; or &#number; ?
In HTML, characters can be represented in three ways:
1. a properly coded character, in the encoding specified by the
"charset" attribute of the "Content-type:" header;
2. a character entity (&entityname;), from the appropriate HTML
specification (HTML 2.0/3.2, HTML 4, etc.);
3. a numeric character reference (&#number;) that specifies the Unicode
reference of the desired character. We recommend using decimal
references; hexadecimal references are less widely supported.
In theory these representations are equally valid. In practice,
authoring convenience and limited support by browsers complicate the
issue.
HTTP being a guaranteed "8-bit clean" protocol, you can safely send
out 8-bit or multibyte coded characters, in the various codings that
are supported by browsers.
A. HTML 2.0/3.2 (Latin-1)
By now there seems no convincing reason to choose &entityname;
versus &#number;, so use whichever is convenient.
If you can confidently handle 8-bit-coded characters this is fine
too, probably preferred for writing heavily-accented languages. Take
care if authoring on non-ISO-8859-based platforms such as Mac,
Psion, IBM mainframes etc., that your upload technique delivers a
correctly coded document to the server. Using &-representations
avoids such problems.
B. A single repertoire other than Latin-1
In such codings as ISO-8859-7 Greek, koi8-r Russian Cyrillic, and
Chinese, Japanese and Korean (CJK) codings, use of coded characters
is the most widely supported and used technique.
Although not covered by HTML 3.2, browsers have supported this quite
widely for some time now; it is a valid option within the HTML 4
specifications--use a validator such as the WDG's online HTML
Validator at <URL:http://www.htmlhelp.com/tools/validator/> which
supports HTML 4 and understands different character encodings.
Browser support for coded characters may depend on configuration and
font resources. In some cases, additional programs called "helpers"
or "add-ins" supply virtual fonts to browsers.
"Add-in" programs have in the past been used to support numeric
references to 15-bit or 16-bit code protocols such as Chinese Big5
or Chinese GB2312.
In theory you should be able to include not only coded characters
but also Unicode numeric character references, but browser support
is generally poor. Numeric references to the "charset-specified"
encoding may appear to produce the desired characters on some
browsers, but this is wrong behavior and should not be used.
Character entities are also problematical, aside from the
HTML-significant characters <, & etc.
C. Internationalization per HTML 4
Recent versions of the popular browsers have support for some of
these features, but at time of writing it seems unwise to rely on
this when authoring for a general audience. If you'd like to explore
the options, you can find comprehensive background documentation and
some practical suggestions at
* http://www.czyborra.com/
* http://www.cs.tut.fi/~jkorpela/chars.html
* http://ppewww.ph.gla.ac.uk/%7Eflavell/charset/
5.4. Should I use lower case or upper case for tags?
Tags are case insensitive, so it doesn't matter. This is just a
matter of style. (You may have noticed that this FAQ is not
absolutely consistent in capitalization.) Many people prefer upper
case, as it makes the tags "stand out" better amongst the text.
Attribute names can also be upper or lower case, as you prefer. But
some attribute values are case sensitive. For example, <OL TYPE=A>
and <OL type=A> are the same, but <OL TYPE=a> is different from both
of them. (For clearer communication, it's worth getting the
terminology right. In this example, OL is the element, TYPE is the
attribute name, and A and a are the attribute values. The tag is <OL
TYPE=A>.)
Entity names like are sometimes incorrectly referred to as
tags. They are all case sensitive. For example, É and
é are two different and valid entities; &NBSP; is invalid.
Note that XHTML 1.0 (a reformulation of HTML 4.01 as an XML 1.0
application) requires element and attribute names to be in lower
case.
5.5. For what screen size should I write?
HTML does not depend on screen size. Normally, the text will be
wrapped by the browser when the end of its display area is
encountered. (Note that graphical browsers are often used with
windows that are smaller than the full area of the screen.)
Preformatted lines (text within <PRE> elements) should only ever
exceed 70 characters if the nature of the content makes it
unavoidable. Longer lines will cause ugly line breaks on text-mode
browsers, and will force horizontal scrolling on graphical browsers.
Readers strongly dislike horizontal scrolling, except where they can
realise that the nature of the content made it inevitable.
Images cannot be wrapped, so you have to be careful with them. It
seems that 400 or 500 pixels is a reasonable width; anything above
600 will mean a certain percentage of users will have to scroll to
see the rightmost bit. This percentage increases with your image
width. Keep in mind that not everyone runs his browser at full
screen!
(WebTV users have no ability to scroll horizontally, so anything
beyond 544 pixels will be compressed by their browser. Some other
devices may be even more limited.)
The use of tables for layout, especially when fixed-width cells are
used, is the most usual single factor that prevents pages from
adapting to various window widths. This is explained in detail at
<URL:http://www.dantobias.com/webtips/tables.html>.
5.6. Why does my page display fine in one browser but incorrectly or not
at all in another?
There are several possibilities.
First, you may have incorrect HTML or CSS syntax. Browsers vary in
their ability to guess what you meant, and different browsers
recover differently from syntax errors. For example, Netscape
Navigator is especially sensitive to invalid table syntax, so a
document with such errors may look fine in other browsers, but not
display at all in NN. See the answer to "How can I check for
errors?"
Second, you may have valid HTML and CSS that different browsers
interpret differently. For example, the CSS specifications allow
conforming browsers to ignore certain properties and property
values. Also, it is not clear from the specifications what should be
done with a string of characters. Some browsers will collapse
them for rendering as a single space; others will render one space
per .
Third, your server may be sending incorrect MIME types for some of
your files. Internet Explorer incorrectly ignores server-provided
MIME types, so it sometimes "does the right thing" when the server
is misconfigured. Other browsers correctly heed the server-provided
MIME types, so they will reveal server misconfigurations. This
includes external style sheets, which should be sent as "text/css".
Fourth, you have have encountered a browser bug. For example, many
common browsers handle CSS better when HTML documents include
optional closing tags like </p> and </li>. Likewise, Netscape
Navigator handles nested tables better when optional closing tags
like </tr>, </th>, and </td> are used, and some versions ignore
frameset documents that define only a single frame.
Another possibility is different user option settings in the
browsers.
See also the answers to "Why are my hyperlinks coming out all wrong
or not loading?" and "Why are my images coming out all wrong or not
loading?"
5.7. Why does the browser show my plain HTML source?
If Microsoft Internet Explorer displays your document normally, but
other browsers display your plain HTML source, then most likely your
web server is sending the document with the MIME type "text/plain".
Your web server needs to be configured to send that filename with
the MIME type "text/html". Often, using the filename extension
".html" or ".htm" is all that is necessary.
See the answer to "Why did my link to a ... file download a bunch of
characters instead?" for more details.
If you are seeing this behavior while viewing your HTML documents on
your local Windows filesystem, then your text editor may have added
a ".txt" filename extension automatically. You should rename
filename.html.txt to filename.html so that Windows will treat the
file as an HTML document.
5.8. How do I freeze the URL displayed in a visitor's browser?
This is a "feature" of using frames: The browser displays the URL of
the frameset document, rather than that of the framed documents.
(See the answer to the question "How do I specify a specific
combination of frames instead of the default document?").
However, this behavior can be circumvented easily by the user. Many
browsers allow the user to open links in their own windows, to
bookmark the document in a specific frame (rather than the frameset
document), or to bookmark links. Thus, there is no reliable way to
stop a user from getting the URL of a specific document.
Furthermore, preventing users from bookmarking specific documents
can only antagonize them. A bookmark or link that doesn't find the
desired document is useless, and probably will be ignored or
deleted.
5.9. How do I put links along the left side of my page?
A common way to do this is to use a two-column table with your links
in the left column and your content in the right column. This is
often combined with a background image that creates a colored strip
on the left behind the links. The background image can tile
vertically, but to avoid horizontal tiling the image should be
extremely wide (e.g., 1600 pixels).
A variation of this technique (which minimizes some of the problems
with using tables for layout) uses a single-cell table with
ALIGN="left". Only the links go inside the table, which floats to
the left. The document's content wraps to fill the space remaining
to the right of and below the table. Here is an example:
<table align="left">
<tr><td><!-- links go here --></td></tr>
</table>
<!-- content goes here -->
Layout tables can be avoided entirely by using CSS. The navigation
links and the page's main content are placed inside separate DIV
elements, and then CSS is used to position these DIV elements
relative to each other. The style sheet can use a smaller background
image that repeats vertically and is aligned along the left, for
example:
body { color: black; background: white url(foo.gif) repeat-y left }
More information about Cascading Style Sheets can be found at:
http://www.htmlhelp.com/reference/css/
Finally, a navigation strip on the left can be implemented with
frames. However, frames introduce problems that are best avoided if
possible.
See the answer to the question, "How do I include one file in
another?" for suggestions that will help you maintain common content
like navigation links across all the documents at your site.
Jakob Nielsen makes some interesting points about the design of site
navigation links in his column, "Is Navigation Useful"
<http://www.useit.com/alertbox/20000109.html>.
5.10. How can I specify colors?
If you want others to view your web page with specific colors, the
most appropriate way is to suggest the colors with a style sheet.
Cascading Style Sheets use the color and background-color properties
to specify text and background colors. To avoid conflicts between
the reader's default colors and those suggested by the author, these
two properties should always be used together. More information
about Cascading Style Sheets can be found at:
http://www.htmlhelp.com/reference/css/
More information about the CSS color property can be found at:
http://www.htmlhelp.com/reference/css/color-background/color.html
More information about the CSS background-color property can be
found at:
http://www.htmlhelp.com/reference/css/color-background/background-color.html
With HTML, you can suggest colors with the TEXT, LINK, VLINK
(visited link), ALINK (active link), and BGCOLOR (background color)
attributes of the BODY element. If one of these attributes is used,
then all of them should be used to ensure that the reader's default
colors do not interfere with those suggested by the author. Here is
an example:
<body bgcolor="#ffffff" text="#000000" link="#0000ff"
vlink="#800080" alink="#000080">
More information about the BODY element can be found at:
http://www.htmlhelp.com/reference/html40/html/body.html
Authors should not rely on the specified colors since browsers allow
their users to override document-specified colors.
5.11. How do I change the color of some text?
The most appropriate way is to use suitable structural markup, and
to suggest the desired color with a style sheet. If you want to
specify a color for only certain cases of an element, then you can
use a class to specify which cases are special. The following CSS
example specifies that emphasized text with the class "special"
should be green (on a white background):
EM.special { color: green; background: white; }
When displayed according to this CSS ruleset, the emphasized text in
the following HTML example will be displayed in green:
normal text <EM CLASS="special">emphasized text</EM> normal text
More information about Cascading Style Sheets can be found at:
http://www.htmlhelp.com/reference/css/
With HTML, the FONT element can also be used to suggest colors. Use
of the FONT element brings numerous usability and accessibility
problems, see: http://www.mcsr.olemiss.edu/%7Emudws/font.html
More information about the FONT element can be found at:
http://www.htmlhelp.com/reference/html40/special/font.html
5.12. How can I specify my scrollbar colors?
Starting with version 5.5, Internet Explorer supports Microsoft's
proprietary CSS properties for scrollbar colors:
scrollbar-3dlight-color, scrollbar-arrow-color,
scrollbar-base-color, scrollbar-darkshadow-color,
scrollbar-face-color, scrollbar-highlight-color, and
scrollbar-shadow-color.
5.13. How can I specify fonts in my Web pages?
If you want others to view your web page with a specific font, the
most appropriate way is to suggest the font rendering with a style
sheet. Cascading Style Sheets use the font-family property to
specify font faces. More information about Cascading Style Sheets
can be found at: http://www.htmlhelp.com/reference/css/
More information about the CSS font-family property can be found at:
http://www.htmlhelp.com/reference/css/font/font-family.html
With HTML, the BASEFONT element can be used to suggest specific
fonts for the entire document. More information about the BASEFONT
element can be found at:
http://www.htmlhelp.com/reference/html40/special/basefont.html
With HTML, the FONT element can also be used to suggest specific
fonts. The FONT element must be repeated inside every block-level
element, since it can contain only inline (text-level) elements. Use
of the FONT element brings numerous usability and accessibility
problems, see: http://www.mcsr.olemiss.edu/%7Emudws/font.html
More information about the FONT element can be found at:
http://www.htmlhelp.com/reference/html40/special/font.html
Whether specifying fonts with CSS or with HTML, authors run the risk
that a reader's system has a font by the same name but which is
significantly different. For example, "Chicago" can be a nice text
font, a display font with letters formed by "bullet holes", or a
novelty font containing images of city buildings (for creating
skylines).
Also, authors must either use fonts (or groups of similar fonts)
that are commonly available on many systems, or provide dynamic
fonts for their readers. Readers who do not have the specified
font(s) installed, or who do not download the dynamic fonts provided
by the author, will see a default font. Some browsers may use a less
legible substitute font than their normal default font in cases
where author-specified fonts are not found.
Netscape and Microsoft have developed competing formats for dynamic
fonts. TrueDoc works on Navigator 4 and (with a plugin) on Internet
Explorer 4+. OpenType works on Internet Explorer 4+. Navigator 6
does not support dynamic fonts. For more information about TrueDoc
(including the WebFont Maker), see:
http://www.truedoc.com/webpages/intro/
For more information about OpenType (including Microsoft's Web
Embedding Fonts Tool (WEFT)), see:
http://www.microsoft.com/typography/web/
For practical advice on using fonts on the web, see Todd Fahrner's
"Beyond the FONT tag: Practical HTML text styling" at:
<http://style.metrius.com/font_size/livetext.html>
Section 6: Hyperlinks
6.1. How do I create a link?
Use an anchor element. The HREF attribute specifies the URL of the
document that you want to link to. The following example links the
text "Web Authoring FAQ" to
<URL:http://www.htmlhelp.com/faq/html/>:
<A HREF="http://www.htmlhelp.com/faq/html/">Web Authoring FAQ</A>
For more information on links and the anchor element, see:
http://www.htmlhelp.com/reference/html40/special/a.html
6.2. How do I link to a location in the middle of an HTML document?
First, identify the destination of the link with a named anchor (an
anchor that uses the NAME attribute). For example:
<H2><A NAME="section2">Section 2: Beyond Introductions</A></H2>
Second, link to the named anchor. The URL of the named anchor is the
URL of the document, with "#" and the name of the anchor appended.
For example, elsewhere in the same document you could use:
<A HREF="#section2">go to Section 2</A>
Similarly, in another document you could use:
<A HREF="thesis.html#section2">go to Section 2 of my thesis</A>
6.3. How do I create a link that opens a new window?
<A TARGET="_blank" HREF=...> opens a new, unnamed window.
<A TARGET="foobar" HREF=...> opens a new window named "foobar",
provided that a window or frame by that name does not already exist.
Note that links that open new windows can be annoying to your
readers if there is not a good reason (from the reader's
perspective) for them.
6.4. How do I create a link that opens a new window of a specific size?
With HTML, there is no way to control the size (or window
decoration, or other features) of a new window. However, in
JavaScript you can specify such details when using the window.open()
function.
Start with a normal HTML link (possibly one that opens in a new
window as described in the answer to the previous question). Then
use the ONCLICK attribute to open a window with the desired
appearance for those readers with JavaScript supported and enabled.
The following example specifies a window named "popup" that is 300
pixels by 150 pixels.
<A HREF="foo.html" TARGET="popup" ONCLICK="window.open('foo.html',
'popup', 'width=300,height=150'); return false">View Foo</A>
Used in this manner, JavaScript can specify a new window with the
desired appearance, without blocking access when JavaScript is
unsupported/disabled.
In addition to the parameters height and width (which take a pixel
count as a value), the third argument to the window.open() can
include the following booloean parameters (which take "yes" or "no"
as a value): directories, location, menubar, resizable, scrollbars,
status, and toolbar. These boolean parameters control the presence
of the corresponding window decorations in the resulting window.
6.5. How do I create a button which acts like a link?
This is best done with a small form:
<FORM ACTION="[URL]" METHOD=GET>
<INPUT TYPE=submit VALUE="Text on button">
</FORM>
If you want to line up buttons next to each other, you will have to
put them in a one-row table, with each button in a separate cell.
Note that search engines might not find the target document unless
there is a normal link somewhere else on the page.
A go-to-other-page button can also be coded in JavaScript, but the
above is standard HTML and works for more readers.
6.6. How do I create a back button on my page?
You cannot do this with HTML. Going "back" means going to the
previous location in your history. You could create a link to the
URL specifed in the HTTP Referer header (available in the
HTTP_REFERER environment variable in CGI programs), but that creates
a link forward to a new location in your history. Even then, the
information in the Referer header can be wrong. Some browsers
incorrectly send the Referer header when the user enters a URL
manually or uses a bookmark. Some never send the Referer header
(which is optional).
You could use JavaScript's history.back() to create a back button
(or link). Naturally, this only works when JavaScript is supported
and enabled.
For a more detailed explanation, please see Abigail's "Simulating
the back button" at
<URL:http://www.foad.org/%7Eabigail/HTML/Misc/back_button.html>.
Also, it is worth noting that the only navigation tool used more
frequently than the "back" function is the hyperlink. Your readers
almost certainly know how to use their browsers' "back" function.
Users who don't know how to use basic functions of their browsers
will only be confused when various pages imitate those functions in
different ways.
6.7. How do I create a button that automatically bookmarks my site?
You cannot do this with HTML. However, Internet Explorer 4+ supports
the window.external.AddFavorite() method, a proprietary extension to
JavaScript that opens an "Add to Favorites" dialog. The following
example avoids creating a non-functional button for those with other
browsers, or for those with JavaScript disabled:
<script type="text/javascript"><!--
function addf() {
window.external.AddFavorite('http://www.htmlhelp.com/',
'Web Design Group'); }
if(document.all) {
document.write('<input type="button" onclick="addf()"'+
' value="Bookmark WDG Site">'); }
//--></script>
It is worth noting that readers who know how to use bookmarks almost
certainly know how to bookmark your site independently. Likewise,
the few readers who don't know how to bookmark your site probably
won't know how to use bookmarks that you create for them. Users who
don't know how to use basic functions of their browsers will only be
confused when various pages imitate those functions in different
ways.
6.8. How do I create a button that prints my page?
You cannot do this with HTML. However, some browsers support the
JavaScript window.print() method, which opens a "Print" dialog. The
following example avoids creating a non-functional button for those
with other browsers, or for those with JavaScript disabled:
<script type="text/javascript"><!--
if (window.print) {
document.write('<input type="button" onclick="window.print()"'+
' value="Print This Page">'); }
//--></script>
It is worth noting that readers who have printers almost certainly
know how to use their browsers' print function. Users who don't know
how to use basic functions of their browsers will only be confused
when various pages imitate those functions in different ways.
6.9. How do I create a link that sends me email?
Use a mailto link, for example
Send me email at
<A HREF="mailto:[email protected]">[email protected]</A>.
Note that any email address that you publish on the WWW like this
will probably start receiving unsolicited commercial email (UCE,
junk email). It's a good idea to protect your real email address
(e.g., by filtering incoming email, or by using a separate address
only for mailto links).
6.10. How do I specify a subject for a mailto link?
You can't, not in any reliable way. The methods that are frequently
posted are not effective on all combinations of browser and email
software (not even on all common combinations), and many of them
have an important drawback: when they fail, the email will be lost.
If you really need a subject, you can do it by providing a form on
your page, which submits data to a CGI program that emails the form
data to you with your desired subject line. However, the form must
have an input field for the visitor's email address, and you must
hope that the visitor enters it correctly.
Here are some other ways to transmit subject-type information:
* Create email aliases that are used only for certain mailto links, so
you'll know that anything sent to a given alias is in response to
the corresponding Web page(s).
* The mail handlers for many Web browsers include an "X-Url" header
that specifies the URL of the Web page that contained the mailto
link. If you configure your mail reader to display this header,
you'll see which Web page the sender is responding to much of the
time.
* Use <A HREF="mailto:user@site" TITLE="Your Subject">. Most browsers
will ignore the TITLE attribute, but some minor browsers will use it
as a subject for the email message. All browsers will send the mail.
* Use <A HREF="mailto:user@site?subject=Your%20Subject">, which puts
"Your Subject" (the space is encoded as "%20") in the "Subject"
header field of the email message in most current browsers. The
details of this RFC can be found at
<URL:http://info.internet.isi.edu/in-notes/rfc/files/rfc2368.txt>.
Note however that you will lose mail from users of older browsers,
so you should consider whether the pre-filled subject is worth lost
mail.
6.11. How do I turn off underlining on my links?
If you want to turn off link underlining when you're looking at
pages in your browser, check your browser's configuration options.
In Netscape 3, for example, see Options | General Preferences |
Appearance; in Netscape 4 it's Edit | Preferences | Appearance |
Colors; in Internet Explorer see View | Options | General.
If you want to prevent links on your page being underlined when your
visitors see them, there's no way in HTML to accomplish this. You
can suggest this presentation using style sheets by defining
a:link, a:visited, a:active {text-decoration: none}
6.12. How can I have two sets of links with different colors?
You can suggest this presentation using style sheets. In your style
sheet, define something like this:
a:link {color: blue; background: white}
a:visited {color: purple; background: white}
a:active {color: red; background: white}
a.foo:link {color: yellow; background: black}
a.foo:visited {color: white; background: black}
a.foo:active {color: red; background: black}
Then use CLASS="foo" to identify the links of the second color in
your HTML, like this:
<A CLASS="foo" HREF=...>...</A>
6.13. How can I make links change when the cursor is over them?
In your style sheet, use the hover pseudo-class to specify a
different appearance for links when the cursor is over them. Specify
the hover pseudo-class after the link and visited pseudo-classes.
For example:
A:link { color: blue ; background: white }
A:visited { color: purple ; background: white }
A:hover { color: red ; background: white }
6.14. Why are my hyperlinks coming out all wrong or not loading?
Your markup may include HTML syntax errors that affect links. For
example, there may not be quotes around attribute values that
require quotes, or there may be a missing closing quote at the end
of the HREF attribute value.
Perfectly valid markup may trigger common browser bugs. For example,
even though a ">" character is valid inside (quoted) attribute
values, several older browsers will think the tag ends there, so the
rest of the tag's attributes are displayed as normal text. Likewise,
">" characters inside comments can trigger similar browser bugs.
(See the answer to "How can I include comments in HTML?" for
practical guidelines.)
As another example, some versions of Netscape Navigator are known to
have problems with links to named anchors when the anchors are
within a table that uses the ALIGN attribute.
It is also possible that your URLs are incorrect. For example, your
web authoring software may have used file URLs (e.g.,
file:C:\path\file.html). If so, then you should replace them with
relative URLs (e.g., file.html) or http URLs (e.g.,
http://example.com/path/file.html).
See the answer to "How can I check for errors?" HTML validators will
find syntax errors in your markup. HTML checkers/linters can find
some syntax errors and valid markup that is known to trigger some
common browser bugs. Link checkers can find links to incorrect URLs.
6.15. Why does my link work in Internet Explorer but not in Netscape?
Is there a space, #, ?, or other special character in the path or
filename? Spaces are not legal in URLs. If you encode the space by
replacing it with %20, your link will work.
You can encode any character in a URL as % plus the two-digit hex
value of the character. (Hex digits A-F can be in upper or lower
case.) According to the spec, only alphanumerics and the special
characters -_.!*'() never need to be encoded.
You should encode all other characters when they occur in a URL,
except when they're used for their reserved purposes. For example,
if you wanted to pass the value "Jack&Jill" to a CGI script, you
would need to encode the "&" character as "%26", which might give
you a URL like the following:
http://www.foo.com/foo.cgi?rhyme=Jack%26Jill&audience=child
Note that the "?" and other "&" character in this URL are not
encoded since they're used for their reserved purposes. However,
when this URL is used as an attribute value in an HTML document, the
"&" character must be encoded as "&", like the following: <A
HREF="http://www.foo.com/foo.cgi?rhyme=Jack%26Jill&audience=child">
For the technical details, see <URL:http://www.w3.org/Addressing/>
Section 7: Images
7.1. How can I display an image on my page?
Use an IMG element. The SRC attribute specifies the location of the
image. The ALT attribute provides alternate text for those not
loading images. For example:
<img src="logo.gif" alt="ACME Products">
For more information on images and the IMG element, see:
http://www.htmlhelp.com/reference/html40/special/img.html
7.2. Which image format should I use?
Here is a simple rule of thumb:
Lots of colors? Use JPEG. Solid colors and sharp lines? Use GIF
(or PNG).
Different image formats compress the image data differently. Their
different compression algorithms have different strengths and
weaknesses. The GIF and PNG formats are excellent with images that
have relatively few colors and no gradations. Most small web
graphics fall into this category. These formats will compress these
images well, and any lettering, lines, and edges in the images will
remain sharp.
On the other hand, the JPEG format is excellent with images where
colors blend smoothly from one to another. Photographs are good
examples, because they usually have many subtle shadows and
variations of color.
For comparisons of the different image formats, see
<URL:http://www.adobe.com/studio/tipstechniques/GIFJPGchart/main.html>
Note that AOL's cache proxy servers convert GIF and JPEG images to
their highly compressed ART image format (*.art) files, and by
default, AOL browsers are configured to use these small, low-quality
versions rather than the originals.
7.3. How do I link an image to something?
Just use the image as the link content, like this:
<A HREF=...><IMG ...></A>
7.4. How can I create a thumbnail image that is linked to the full-sized
image?
A thumbnail image is just a copy of the full-sized image that has
been modified to reduce the size of the file. It is linked to the
full-sized image with a normal link:
<A HREF="full-sized.jpg"><IMG SRC="thumbnail.jpg" ALT=...></A>
There are several techniques for reducing the size of the file for
the thumbnail image, including
* resampling/resizing the image to create a physically smaller image;
* cropping the image to remove less significant parts of the image;
* reducing the image quality to increase compression ratios; and
* reducing the size of the color palette (e.g., converting to
greyscale).
Thumbnail images can use multiple techniques simultaneously. For
example, Jakob Nielsen advocates "Relevance-Enhanced Image
Reduction", which combines resampling/resizing and cropping.
7.5. How do I link different parts of an image to different things?
Use an image map. Client-side image maps don't require server-side
processing, so response time is faster. Server-side image maps hide
the link definitions from the browser, and can act as a backup for
client-side image maps for the few very old browsers that support
server-side image maps but not client-side image maps.
The configuration details of server-side image maps vary from server
to server. Refer to your server documentation for details.
Client-side image maps are implemented with HTML. The MAP element
defines an individual image map and the AREA element defines
specific linked areas within that image map. The USEMAP attribute of
the IMG element associates an image map with a specific image. A
detailed explanation (with examples) is available at
<http://www.htmlhelp.com/reference/html40/special/map.html>. A
tutorial is available at
<http://ppewww.ph.gla.ac.uk/%7Eflavell/www/imgmaptut.html>.
7.6. How do I eliminate the blue border around linked images?
Use the BORDER="0" attribute in the <IMG> element. For example:
<A HREF="doc.html"><IMG SRC="doc.gif" ALT="View document."
BORDER="0"></A>
7.7. Why am I getting a colored whisker to the left or right of my
image?
This is the result of including "white space" (spaces and newlines)
before or after an IMG inside an anchor. For example:
<A HREF=...>
<IMG SRC=...>
</A>
will have white space to the left and right of the image. Since many
browsers display anchors with colored underscores by default, they
will show the spaces to the left and right of the image with colored
underscores.
Solution: don't leave any white space between the anchor tags and
the IMG tag. If the line gets too long, break it inside the tag
rather than outside it, like this:
<A HREF=...><IMG
SRC=...></A>
Style checkers such as Weblint will call attention to this problem
in your HTML source.
7.8. How do I eliminate the space around/between my images?
If your images are inside a table, be sure to set the BORDER,
CELLSPACING, and CELLPADDING attributes to 0.
Also, extra space between images is often created by whitespace
around the <IMG> tag in the markup. It is safe to use newlines
inside a tag (between attributes), but not between two tags. For
example, replace this:
<TD ...>
<IMG SRC=... ALT=...>
<IMG SRC=... ALT=...>
<IMG SRC=... ALT=...>
<IMG SRC=... ALT=...>
</TD>
with this:
<TD ...><IMG SRC=... ALT=...><IMG SRC=... ALT=...><IMG SRC=...
ALT=...><IMG SRC=... ALT=...></TD>
According to the latest specifications, the two should be
equivalent. However, common browsers do not comply with the
specifications in this situation.
7.9. Why are my images coming out all wrong or not loading?
Most likely you forgot to close a quote at the end of the SRC
attribute. Alternatively, perhaps you used a ">" character in an ALT
text or somewhere else inside a tag. Although this is legal, several
older browsers will think the tag ends there, so the rest is
displayed as normal text.
This especially happens if you use comment tags to "comment out"
text with HTML tags. (See the answer to "How can I include comments
in HTML?") Although the correct syntax is <!-- --> (without "--"
occurring anywhere inside the comment), some browsers will think the
comment ends at the first ">" they see.
Validators will show you any syntax errors in your markup, but
checkers such as Weblint and HTMLchek can show you where you are
liable to provoke known browser bugs. See also the answer to "How
can I check for errors?"
Here are some other possibilities:
* Your web authoring software may have used file URLs (e.g.,
file:C:\path\image.gif). If so, then you should replace them with
relative URLs (e.g., image.gif) or http URLs (e.g.,
http://server/path/image.gif).
* Your images may be in a format that is not widely supported, like
Microsoft's BMP format or AOL's ART format. Be sure to save your
images in a widely supported format like GIF, JPEG, or PNG. (Note
that you need to convert the image data format; you can't just
rename the file.)
7.10. How do I make animated GIFs?
Check out the following resources:
* http://members.aol.com/royalef/gifanim.htm
* http://www.webreference.com/dev/gifanim/
7.11. How can I display random images?
There are two basic approaches. The most cache-friendly method is to
use a normal IMG tag that refers to a CGI script that randomly
redirects the browser to one of several images. There is an example
of such a CGI script at
<URL:http://www.foad.org/%7Eabigail/CGI/random_images.html>. See the
CGI Programming FAQ <URL:http://www.htmlhelp.com/faq/cgifaq.html>
for more information about CGI.
The second method is to generate the HTML dynamically using a
mechanism like Server Side Includes (SSI) or CGI. This method is
less cache-friendly, but it does allow the surrounding markup (e.g.,
HEIGHT and WIDTH attributes, or the URLs for linked/image-mapped
images) to vary with the image. If your server supports SSI, the
details can be found in your server documentation.
7.12. How do I prevent people from saving my images?
You can't. The image file is necessary for the browser to display
your document; you must send it to the browser. Even if a particular
browser doesn't have a "Save Image" feature, there are many that do,
and someone can always retrieve the image file by hand (using
telnet) or from the browser's cache.
There are tricks that make it more difficult for some readers to
save your images. However, just as with tricks that try to hide HTML
source, these tricks cause various problems for law-abiding users
and can't really prevent thieves from saving your images.
7.13. Can I put markup in ALT text?
No. Character entities (©, &#nnn; and such) are permitted,
though.
If you want to know how to write good ALT texts without markup,
please see Alan Flavell's essay on choosing ALT texts at
<URL:http://www.htmlhelp.com/feature/art3.htm>.
7.14. How do I align an image to the right (or left)?
You can use <img align="right"> to float a image to the right. (Use
align="left" to float it to the left.) Any content that follows the
<img> tag will flow around the image. Use <br clear="right"> or <br
clear="all"> to mark the end of the text that is to flow around the
image, as shown in this example:
<img align="right" src=... alt=...>
The image will float to the right. This text will wrap to fill the
available space to the left of (and if the text is long enough,
below) the image.
<br clear="right">
This text will appear below the image, even if there is additional
room to its left.
For an explanation with nice examples, see
<URL:http://www.awpa.asn.au/html/images.html>.
7.15. How can I specify background images?
If you want others to view your web page with a background image,
the most appropriate way is to suggest the background with a style
sheet. Cascading Style Sheets use the background-image property to
specify a background image. More information about Cascading Style
Sheets can be found at: http://www.htmlhelp.com/reference/css/
More information about the CSS background-image property can be
found at:
http://www.htmlhelp.com/reference/css/color-background/background-image.html
With HTML, you can suggest a tiled background image with the
BACKGROUND attribute of the BODY element. Here is an example:
<body background="imagefile.gif" bgcolor="#ffffff" text="#000000"
link="#0000ff" vlink="#800080" alink="#000080">
More information about the BODY element can be found at:
http://www.htmlhelp.com/reference/html40/html/body.html
If you specify a background image, you should also specify text,
link, and background colors (see the answer to the question "How can
I specify colors?") since the reader's default colors may not
provide adequate contrast against your background image. The
background color will be used by those not loading images. Authors
should not rely on the specified background image since browsers
allow their users to disable image loading or to override
document-specified backgrounds.
7.16. How do I have a fixed background image?
Use a style sheet with the following ruleset:
body { color: black; background: white url(foo.gif) fixed }
Note that the background: fixed property used in the above style
sheet is supported by Internet Explorer 3+, Netscape Navigator 5+,
Opera 3.6+, and other browsers. In contrast, the proprietary
BGPROPERTIES=fixed attribute is supported only by Internet Explorer
3+.
7.17. How do I have a non-tiled background image?
Use a style sheet with the following ruleset:
body { color: black; background: white url(foo.gif) no-repeat }
Section 8: Other Media
8.1. How do I let people download a file from my page?
Once the file is uploaded to the server, you need only use an anchor
reference tag to link to it. An example would be:
<a href="../files/foo.zip">Download Foo Now! (100kb ZIP)</a>
It is possible that the server might need to be configured for some
different file types. (See the next Q&A.)
8.2. Why did my link to a ... file download a bunch of characters
instead?
If you are trying to link to a particular type of file and it is not
returning your desired response, chances are that the server needs
to have the type configured. Talk to your system administrator about
getting them to add the content type. Here is a list of common types
that often need configuring:
Content Type Description
Application/msword Microsoft Word Document
application/octet-stream Unclassified binary data (often used for
compressed file or executable)
application/pdf PDF Document
application/wordperfect6.0 WordPerfect 6.0 Document
application/zip ZIP archive
audio/x-wav WAV audio format
audio/midi MIDI audio format
audio/x-pn-realaudio RealAudio
image/gif GIF image format
image/jpeg JPEG image format
image/png PNG image format
text/css CSS style sheet
text/html HTML document
text/plain Plain text
video/mpeg MPEG video format
video/quicktime QuickTime video format
video/x-msvideo AVI video format
Another method of ensuring that your file is properly sent to the
client is to compress it into a standard compression format.
Virtually all servers are set to handle the .zip extension and it is
widely recognized by users.
Some servers (NCSA, Apache, and others) can be configured to support
user-configured content types. Details are server dependent, so
consult your server admin or documentation.
Note that Internet Explorer incorrectly ignores server-provided MIME
types, so it sometimes "does the right thing" when the server is
misconfigured. Other browsers correctly heed the server-provided
MIME types, so they will reveal server misconfigurations.
8.3. How do I force the browser to download a file? How do I force the
browser to show/play a file itself? How do I force a file to be opened
by a particular program?
You can't do any of these things reliably, because the Web doesn't
work that way. See
<URL:http://www.dantobias.com/webtips/force.html>.
When the browser requests a document (hypertext, image, audio,
multimedia, etc.), the server tells the browser what type of file it
is. The server should be configured to identify a document's media
type properly, as described in the answer to the previous question.
The browser then decides what to do with it. Different browsers are
able to and are configured to display different types of documents
themselves. Browsers are usually configured to handle other file
types by using appropriate helper applications or by offering to
save the document to the filesystem.
RFC 2183 describes the Content-disposition header, which can be used
to suggest how the browser should handle documents. The value
"inline" suggests that the document should be displayed
automatically, and the value "attachment" suggests that the user
should prompted before the document is displayed (or saved). Note
that this mechanism has significant security implications, which are
described in the RFC.
Most browsers allow users to download to disk if they want to. If
the file must be saved to disk, if there is absolutely no other way
to handle it, then the MIME type could be
"application/octet-stream". However, this essentially says, "I can't
or won't tell you what this is." Furthermore, the MIME type
"application/octet-stream" provokes incorrect behavior in MSIE's
HTTP implementation. A better alternative would be a custom MIME
type like "application/x-some-explanation", which avoids these
problems.
8.4. How do I get an audio file to play automatically when someone
visits my site?
Most browsers support the EMBED element for this, provided that the
user has a suitable plug-in for the sound file. You can reach a
slightly wider audience if you use BGSOUND as well. To avoid
problems with browsers that support both, place the BGSOUND in a
NOEMBED container:
<EMBED SRC="your_sound_file" HIDDEN=true AUTOSTART=true>
<NOEMBED><BGSOUND SRC="your_sound_file"></NOEMBED>
For more on the EMBED element, see
<URL:http://developer.netscape.com/docs/manuals/htmlguid/tags14.htm#1286379>.
For more on the BGSOUND element, see
<URL:http://msdn.microsoft.com/workshop/author/dhtml/reference/objects/bgsound.asp>.
Note that these elements are proprietary and not in any HTML
standard. (The HTML standard way of doing this is not well
supported.)
Be aware that some users find it annoying for music to automatically
start playing. They may not have the volume set properly on their
speakers, or they may be listening to something else. As a courtesy
to your users, you may prefer to offer the sound file as a link:
<A HREF="your_sound_file">Listen to my sound! (5 kB MIDI)</A>
8.5. How can I strip all the HTML from a document to get plain text?
Many browsers have a "Save As..." function that allows you to
specify plain text as the output format. Another approach is to
select all the text, copy it to the clipboard, and paste it into an
editor.
Lynx users can use "lynx -dump http://..." on the command line to
print to file and append a list of referenced URLs as footnotes. If
you want the output file without the footnotes, use the "p" command
to "print" to a text file.
Some HTML authoring tools have an option to strip all HTML as well.
Two programs of note are
* HomeSite, available from <URL:http://www.allaire.com/>
* DiDa, available from <URL:http://www.faico.net/>
If you are looking for another method (in other words you want to
make things more difficult on yourself), you can obtain programs
which will strip away all HTML markup from a document. Try doing a
search at <URL:http://www.altavista.com/> for the phrase "HTML
stripper".
Section 9: Presentational Effects
9.1. How can I make a custom rule?
Your best option is likely a centered IMG with a line of "--"
characters as ALT text:
<P ALIGN=center><IMG SRC="custom-line.gif"
ALT="--------------------"></P>
For an experimental but somewhat more graceful approach, read about
CSS1 and the Decorative HR at
<URL:http://ppewww.ph.gla.ac.uk/%7Eflavell/www/hrstyle.html>.
9.2. How can I make a list with custom bullets?
There are several methods, none completely satisfactory:
* Use the list-style property of Cascading Style Sheets. This should
be the preferred method of using custom bullets, but unfortunately
it's not widely supported by browsers. However, non-supporting
browsers will see a normal bullet, so using this method today is not
a problem. See <URL:http://www.htmlhelp.com/reference/css/> for
more information on style sheets.
* Use a <DL> with <DD> tags with preceding images (with ALIGN and
suitable ALT text) and no <DT>; this won't be as beautiful as a
"real" list.
* Use a two-column table, with the bullets in the left column and the
text in the right. Since browsers show nothing before downloading
the entire table, this can be slow with long lists.
* Create the bullet with the indent built in. For example, if you use
a bullet that is 10 pixels across you can make the background 25
pixels (transparent) and put the bullet all the way on the right.
This will create a 15-pixel indent to the left of the bullet. It
will add slightly to the byte size of the graphic but since it is
all one color it won't add much. This method doesn't work well with
any list items that are longer than a line (and remember that you
don't know how long a line will be on the visitor's screen).
9.3. Where can I get a "hit counter"?
A hit counter is a small script or program that increases a number
every time a document is accessed from the server.
Why do you want one? If you believe that it will tell you how many
times your documents have been accessed, you are mistaken. No
counter can keep track of accesses from browser caches or proxy
caches. Some counters depend on image-loading to increment; such
counters ignore accesses from text-mode browsers, or browsers with
image-loading off, or from users who interrupted the transfer. Some
counters even require access to a remote site, which may be down or
overloaded, causing a delay in displaying your documents.
Most web servers log accesses to documents stored on the server
machine. These logs may be processed to gain information about the
*relative* number of accesses over an extended period. There is no
reason to display this number to your viewers, since they have no
reference point to relate this number to. Not all service providers
allow access to server logs, but many have scripts that will output
information about accesses to a given user's documents. Consult your
sysadmin or service provider for details.
Counter services and information are available from Yahoo's list of
counters:
http://dir.yahoo.com/Computers_and_Internet/Internet/World_Wide_Web/Programming/Access_Counters/
A discussion of the limitations of web-traffic statistics is at
<URL:http://www.goldmark.org/netrants/webstats/>
9.4. How do I display the current date or time in my document?
With server-side includes. Ask your webmaster if this is supported,
and what the exact syntax is for your server. But this will display
the local time on the server, not for the client. And if the
document is cached, the date will of course be incorrect after some
time. JavaScript can be used to display the local time for the
client, but again, as most people already have one or more clocks
on their screen, why display another one?
If you plan on putting the current date or time on your pages,
using a CGI, JavaScript or VBScript, take an extra breath and
consider that it will take resources, add time to the loading of
the page, and prevent good caching. If you find that you really
have a need to use it, for instance to inform readers of the
up-times of an FTP server, then by all means do so. If, on the
other hand, your only reason is 'it looks cool!' - then reconsider.
9.5. How do I get scrolling text in the status bar?
This is not an HTML question; it's done with JavaScript. Check any
page which has this feature, and copy the script from the source.
This script has two big problems. One, usually it uses the
decrement operator (c--) at some point. The "--" sequence in a
comment actually closes it on some browsers, so your code may
"leak" on those browsers. The same goes for ">".
Second, keep in mind that many people consider this even worse than
<BLINK>, and that it also suppresses the status information which
normally appears there. It prevents people from knowing where a
link goes to.
9.6. How do I right align or justify text?
The HTML solution is to use the ALIGN="right" attribute on
paragraphs, divisions, headings, etc. This will right align your
text (ragged left). Note that the ALIGN attribute is deprecated by
HTML 4 in most contexts.
The CSS mechanism is to use the text-align: right property in your
ruleset. This example right aligns all paragraphs with the
class="note" attribute:
p.note {text-align: right}
Perhaps what you really want is justified text, in which the left
and right edges are both aligned so that all lines are the same
length. (This is sometimes incorrectly called "right justify".)
This presentation can be suggested in HTML with the ALIGN="justify"
attribute. This CSS example justifies all paragraphs with the
class="adcopy" attribute:
p.adcopy {text-align: justify}
Before you justify text, there are some caveats. Although justified
text may look pretty, human factors analysis shows that ragged
right is actually easier to read and understand. Furthermore,
browser bugs and poor implementations may further reduce the
legibility of your text.
For more information, see
<URL:http://www.cs.tut.fi/~jkorpela/www/justify.html>.
9.7. How do I indent the first line in my paragraphs?
Use a style sheet with the following ruleset:
P { text-indent: 5% }
See <URL:http://www.htmlhelp.com/reference/css/> for more
information on style sheets.
9.8. How do I indent a lot of text?
Use a style sheet to set a left margin for the whole document or
part of it:
/* Entire document */
BODY { margin-left: 20% }
/* Part of a document with CLASS="foo" */
.foo { margin-left: 15% }
See <URL:http://www.htmlhelp.com/reference/css/> for more
information on style sheets.
9.9. How do I eliminate the margins around my page?
The most appropriate way is to use a style sheet to specify margin
and padding properties. More information about Cascading Style
Sheets can be found at: http://www.htmlhelp.com/reference/css/
With proprietary HTML extensions, you can set the margins for
certain browsers. Internet Explorer 3+ supports the TOPMARGIN and
LEFTMARGIN attributes. Internet Explorer 4+ added support for the
BOTTOMMARGIN and RIGHTMARGIN attributes. Navigator 4+ supports the
MARGINWIDTH and MARGINHEIGHT attributes. Most other browsers ignore
these proprietary extensions.
CSS and proprietary HTML can be combined. The following is
effective in most browsing situations:
<body marginheight="0" topmargin="0" marginwidth="0" leftmargin="0"
style="margin:0;padding:0">
More information is available at
<URL:http://www.cs.tut.fi/~jkorpela/www/margins.html
Also note that Navigator always leaves room for a scrollbar on the
right, but draws the scrollbar only when the document is long
enough to require scrolling. If the document does not require
scrolling, then this leaves a right "margin" that cannot be
removed.
9.10. How do I do a page break?
Page breaks are offered in Cascading Style Sheets, Level 2, but
they are not well supported by browsers. See
<URL:http://www.w3.org/TR/REC-CSS2/page.html#page-breaks> for
information on CSS2 page breaks.
In general, page breaks are not appropriate on the Web since what
makes a nice page break for you with your font and font size may be
a poor page break for me with my font and font size.
If you need to produce a nicely formatted printed copy of your HTML
documents, you might also consider using special purpose tools
rather than your browser's Print function. For example, html2ps
generates nicely formatted PostScript output from HTML documents,
and HTML Scissor uses special HTML comments for suggesting page
breaks.
9.11. How can I have a custom icon when people bookmark my site?
This is a feature introduced by Internet Explorer 5.x. By default,
the browser requests a file named "favicon.ico" at the same base
URL as the document being bookmarked. If it doesn't find this file,
then it will try again in the root directory of your site. Web
authors can specify a different path for the icon file with a
<LINK> element like this: <LINK REL="SHORTCUT ICON"
HREF="/pathname/filename.ico">
The image should be 16 by 16 pixels, in the Windows icon format. If
your graphics program doesn't support the Windows icon format, you
can use a tool like the free Java-based icon generator at
<URL:http://www.favicon.com/> to convert/create your icon.
For further information, see
<URL:http://msdn.microsoft.com/workshop/Author/dhtml/howto/ShortcutIcon.asp>
or search for "favicon.ico" at
<URL:http://msdn.microsoft.com/workshop/essentials/versions/ICPIE5.asp>
Section 10: HTML Tables
10.1. How do I make a table which looks good on non-supporting
browsers?
See Alan Flavell's document on tables for a good discussion at
<URL:http://ppewww.ph.gla.ac.uk/%7Eflavell/www/tablejob.html>.
10.2. Can I nest tables within tables?
Yes, a table can be embedded inside a cell in another table. Here's
a simple example:
<table>
<tr>
<td>this is the first cell of the outer table</td>
<td>this is the second cell of the outer table,
with the inner table embedded in it<br>
<table>
<tr>
<td>this is the first cell of the inner table</td>
<td>this is the second cell of the inner table</td>
</tr>
</table>
</td>
</tr>
</table>
The main caveat about nested tables is that many versions of
Netscape Navigator have problems with them if you don't explicitly
close your TR, TD, and TH elements. To avoid problems, include
every </tr>, </td>, and </th> tag, even though the HTML
specifications don't require them.
Also, many versions of Navigator have problems with tables that are
nested extremely deeply (e.g., tables nested ten deep). To avoid
problems, avoid nesting tables more than a few deep. You may be
able to use the ROWSPAN and COLSPAN attributes to minimize table
nesting.
Finally, be especially sure to validate your markup whenever you
use nested tables.
10.3. How can I use tables to structure forms?
Small forms are sometimes placed within a TD element within a
table. This can be a useful for positioning a form relative to
other content, but it doesn't help position the form-related
elements relative to each other.
To position form-related elements relative to each other, the
entire table must be within the form. You cannot start a form in
one TH or TD element and end in another. You cannot place the form
within the table without placing it inside a TH or TD element. You
can put the table inside the form, and then use the table to
position the INPUT, TEXTAREA, SELECT, and other form-related
elements, as shown in the following example.
<FORM ACTION="[URL]">
<TABLE BORDER="0">
<TR>
<TH>Account:</TH>
<TD><INPUT TYPE="text" NAME="account"></TD>
</TR>
<TR>
<TH>Password:</TH>
<TD><INPUT TYPE="password" NAME="password"></TD>
</TR>
<TR>
<TD> </TD>
<TD><INPUT TYPE="submit" NAME="Log On"></TD>
</TR>
</TABLE>
</FORM>
10.4. How do I center a table?
The "correct" way of doing it is <TABLE ALIGN=CENTER>, but this
doesn't work in several popular browsers. Put <CENTER>; around the
entire table for these browsers.
This causes some problems with browsers that do support CENTER but
not tables, such as Lynx. In these browsers, the contents of the
cells are now displayed centered, which is not what is intended. To
avoid this, you can put the cell's contents in <P ALIGN=left> or
<DIV ALIGN=left> depending on the amount of text in the cell.
10.5. How do I align a table to the right (or left)?
You can use <TABLE ALIGN="right"> to float a table to the right.
(Use ALIGN="left" to float it to the left.) Any content that
follows the closing </TABLE> tag will flow around the table. Use
<BR CLEAR="right"> or <BR CLEAR="all"> to mark the end of the text
that is to flow around the table, as shown in this example:
<table align="right">...</table>
The table will float to the right. This text will wrap to fill the
available space to the left of (and if the text is long enough,
below) the table.
<br clear="right">
This text will appear below the table, even if there is additional
room to its left.
10.6. Can I use percentage values for <TD WIDTH=...>?
The HTML 3.2 and HTML 4.0 specifications allow only integer values
(representing a number of pixels) for the WIDTH attribute of the TD
element. However, the HTML 4.0 DTD allows percentage (and other
non-integer) values, so an HTML validator will not complain about
<TD WIDTH="xx%">.
It should be noted that Netscape and Microsoft's browsers interpret
percentage values for <TD WIDTH=...> differently. However, their
interpretations (and those of other table-aware browsers) happen to
match when combined with <TABLE WIDTH="100%">. In such situations,
percentage values can be used relatively safely, even though they
are prohibited by the public specifications.
10.7. Why doesn't <TABLE WIDTH="100%"> use the full browser width?
Graphical browsers leave a narrow margin between the edge of the
display area and the content. For information on how you can
specify that the browser omit these margins, see the answer to the
question "How do I eliminate the margins around my page?"
Also note that Navigator always leaves room for a scrollbar on the
right, but draws the scrollbar only when the document is long
enough to require scrolling. If the document does not require
scrolling, then this leaves a right "margin" that cannot be
removed.
10.8. Why is there extra space before or after my table?
This is often caused by invalid HTML syntax. Specifically, it is
often caused by loose content within the table (i.e., content that
is not inside a TD or TH element). There is no standard way to
handle loose content within a table. Some browsers display all
loose content before or after the table. When the loose content
contains only multiple line breaks or empty paragraphs, then these
browsers will display all this empty space before or after the
table itself.
The solution is to fix the HTML syntax errors. All content within a
table must be within a TD or TH element.
10.9. Are there any problems with using tables for layout?
On current browsers, the entire table must be downloaded and the
dimensions of everything in the table must to be known before the
table can be rendered. That can delay the rendering of your
content, especially if your table contains images without HEIGHT or
WIDTH attributes.
If any of your table's content is too wide for the available
display area, then the table stretches to accomodate the oversized
content. The rest of the content then adjusts to fit the oversized
table rather than fitting the available display area. This can
force your readers to scroll horizontally to read your content, or
can cause printed versions to be cropped.
For readers whose displays are narrower than the author
anticipated, fixed-width tables cause the same problems as other
oversized tables. For readers whose displays are wider than the
author anticipated, fixed-width tables cause extremely wide
margins, wasting much of the display area. For readers who need
larger fonts, fixed-width tables can cause the content to be
displayed in short choppy lines of only a few words each.
Many browsers are especially sensitive to invalid syntax when
tables are involved. Correct syntax is especially critical. See the
answer to "How can I check for errors?" Even with correct syntax,
nested tables may not display correctly in Netscape. See the answer
to "Can I nest tables within tables?" for what you can do about
that.
Some browsers ignore tables, or can be configured to ignore tables.
These browsers will ignore any layout you've created with tables.
Also, search engines ignore tables. Some search engines use the
text at the beginning of a document to summarize it when it appears
in search results, and some index only the first n bytes of a
document. When tables are used for layout, the beginning of a
document often contains many navigation links that appear before
than actual content.
Many versions of Navigator have problems linking to named anchors
when they are inside a table that uses the ALIGN attribute. These
browsers seem to associate the named anchor with the top of the
table, rather than with the content of the anchor. You can avoid
this problem by not using the ALIGN attribute on your tables.
If you use tables for layout, you can still minimize the related
problems with careful markup. Avoid placing wide images, PRE
elements with long lines, long URLs, or other wide content inside
tables. Rather than a single full-page layout table, use several
independent tables. For example, you could use a table to lay out a
navigation bar at the top/bottom of the page, and leave the main
content completely outside any layout tables.
The use of tables for layout is explored in detail at
<URL:http://www.dantobias.com/webtips/tables.html>.
Section 11: HTML Forms
11.1. How do I use forms?
The basic syntax for a form is: <FORM ACTION="[URL]">...</FORM>
When the form is submitted, the form data is sent to the URL
specified in the ACTION attribute. This URL should refer to a
server-side (e.g., CGI) program that will process the form data.
The form itself should contain
* at least one submit button (i.e., an <INPUT TYPE="submit" ...>
element),
* form data elements (e.g., <INPUT>, <TEXTAREA>, and <SELECT>) as
needed, and
* additional markup (e.g., identifying data elements, presenting
instructions) as needed.
A more detailed explanation of the use of forms is available at
<URL:http://www.cs.tut.fi/~jkorpela/forms/>. If you want to install
CGI programs on your server, the following are useful resources:
* the CGI Programming FAQ
<URL:http://www.htmlhelp.com/faq/cgifaq.html>
* the CGI section of the W3C's Security FAQ
<URL:http://www.w3.org/Security/faq/wwwsf4.html>
* the list of prewritten CGI scripts/programs at
<URL:http://www.cgi-resources.com/Programs_and_Scripts/>
11.2. How do I get form data emailed to me?
The only reliable mechanism for processing form submissions is with
a server-side (e.g., CGI) program. To send form data to yourself
via email, you should use a server-side program that processes the
form submission and sends the data to your email address.
Some web service providers make standard form-to-email programs
available to their customers. Check with your service provider for
details.
If you can install CGI programs on your own server, see the answer
to the previous question for a list of useful resources.
If you can't run CGI programs on your own server, you can use a
remotely hosted form-to-email services. A list of such services can
be found at
<URL:http://cgi.resourceindex.com/Remotely_Hosted/Form_Processing/>.
Note that the provider of a remotely hosted service will have
access to any data submitted via the service.
Forms that use ACTION="mailto:..." are unreliable. They may work
for some of your users, but they will fail for others who have
different software configurations.
11.3. How can I use tables to structure forms?
Small forms are sometimes placed within a TD element within a
table. This can be a useful for positioning a form relative to
other content, but it doesn't help position the form-related
elements relative to each other.
To position form-related elements relative to each other, the
entire table must be within the form. You cannot start a form in
one TH or TD element and end in another. You cannot place the form
within the table without placing it inside a TH or TD element. You
can put the table inside the form, and then use the table to
position the INPUT, TEXTAREA, SELECT, and other form-related
elements, as shown in the following example.
<FORM ACTION="[URL]">
<TABLE BORDER="0">
<TR>
<TH>Account:</TH>
<TD><INPUT TYPE="text" NAME="account"></TD>
</TR>
<TR>
<TH>Password:</TH>
<TD><INPUT TYPE="password" NAME="password"></TD>
</TR>
<TR>
<TD> </TD>
<TD><INPUT TYPE="submit" NAME="Log On"></TD>
</TR>
</TABLE>
</FORM>
11.4. How can I eliminate the extra space after a </form> tag?
HTML has no mechanism to control this. However, with CSS, you can
set the margin-bottom of the form to 0. For example:
<form style="margin-bottom:0;" action=...>
You can also use a CSS style sheet to affect all the forms on a
page:
form { margin-bottom: 0 ; }
Further discussion is available at
<URL:http://www.cs.tut.fi/~jkorpela/forms/extraspace.html>.
11.5. How do I make a form so it can be submitted by hitting ENTER?
The short answer is that the form should just have one <INPUT
TYPE=TEXT> and no TEXTAREA, though it can have other form elements
like checkboxes and radio buttons. For a more detailed answer, see
<URL:http://ppewww.ph.gla.ac.uk/%7Eflavell/www/formquestion.html>.
11.6. How do I set the focus to the first form field?
You cannot do this with HTML. However, you can include a script
after the form that sets the focus to the appropriate field, like
this:
<FORM ID="myform" NAME="myform" ACTION=...>
<INPUT TYPE="text" ID="myinput" NAME="myinput" ...>
</FORM>
<script type="text/javascript"><!--
document.myform.myinput.focus();
//--></script>
A similar approach uses <BODY ONLOAD=...> to set the focus, but
some browsers seem to process the ONLOAD event before the entire
document (i.e., the part with the form) has been loaded.
11.7. How can I make a form with custom buttons?
Rather than a normal submit button (<input type="submit" ...>), you
can use the image input type (<input type="image" ...>). The image
input type specifies a graphical submit button that functions like
a server-side image map.
Unlike normal submit buttons (which return a name=value pair), the
image input type returns the x-y coordinates of the location where
the user clicked on the image. The browser returns the x-y
coordinates as name.x=000 and name.y=000 pairs.
For compatability with various non-graphical browsing environments,
the VALUE and ALT attributes should be set to the same value as the
ALT attribute. For example:
<input type="image" name="Send" alt="Send" value="Send"
src="send-button.gif">
For more information, see
<URL:http://ppewww.ph.gla.ac.uk/%7Eflavell/www/trysub.html> and
<URL:http://www.cs.tut.fi/~jkorpela/forms/imagebutton.html>.
For the reset button, one could use <button type="reset" ...>,
JavaScript, and/or style sheets, although none of these mechanisms
work universally. For more information, see
<URL:http://www.cs.tut.fi/~jkorpela/forms/imagereset.html>.
11.8. Can I have two or more Submit buttons in the same form?
Yes. This is part of HTML 2.0 Forms support (some early browsers
did not support it, but browser coverage is now excellent).
The submit buttons must have a NAME attribute. The optional VALUE
attribute can be used to specify different text for the different
submit buttons.
To determine which submit button was used, you need to use
different values for the NAME and/or VALUE attributes. Browsers
will send to the server the name=value pair of the submit button
that was used. Here is an example:
<input type="submit" name="join" value="I want to join now">
<input type="submit" name="info" value="Please send full details">
Note that if you are using image submit buttons, you need to
provide different NAME attributes for them too.
If you're unsure what results you're going to get when you submit
your form, TipJar has a standard script which you can use. Code
this, for example (assuming method "post"):
<form method="post" action="http://www.tipjar.com/cgi-bin/test">
and then go through the motions of submitting your form. The TipJar
server decodes the form input, and displays the result to you.
11.9. Can I have two or more actions in the same form?
No. A form must have exactly one action. However, the server-side
(e.g., CGI) program that processes your form submissions can
perform any number of tasks (e.g., updating a database, sending
email, logging a transaction) in response to a single form
submission.
11.10. How can I require that fields be filled in, or filled in
correctly?
Have the server-side (e.g., CGI) program that processes the form
submission send an error message if the field is not filled in
properly. Ideally, this error message should include a copy of the
original form with the original (incomplete or incorrect) data
filled in as the default values for the form fields. The Perl
CGI.pm module provides helpful mechanisms for returning partially
completed forms to the user.
In addition, you could use JavaScript in the form's ONSUBMIT
attribute to check the form data. If JavaScript support is enabled,
then the ONSUBMIT event handler can inform the user of the problem
and return false to prevent the form from being submitted.
Note that the server-side program should not rely upon the checking
done by the client-side script.
11.11. Can I prevent a form from being submitted again?
No. The server-side (e.g., CGI) program that processes the form
submission must handle duplicate submissions gracefully.
You could generate the form with a server-side (e.g., CGI) program
that adds a hidden field with a unique session ID. Then the
server-side program that processes the form submission can check
the session ID against a list of previously used session IDs. If
the session ID has already been used, then an appropriate action
can be taken (e.g., reject the submission, or update the previously
submitted data).
11.12. How can I allow file uploads to my web site?
First of all, the RFC for this is located at
<URL:http://www.ics.uci.edu/pub/ietf/html/rfc1867.txt>.
File upload is handled by the Perl CGI.pm module available from
<URL:http://stein.cshl.org/WWW/software/CGI/cgi_docs.html>. The
most recent versions of the cgi-lib.pl library also support file
upload.
These things are necessary for Web-based uploads:
* An HTTP server that accepts uploads.
* Access to the /cgi-bin/ to put the receiving script. Prewritten CGI
file-upload scripts are available.
* A form implemented something like this:
<form method="post" enctype="multipart/form-data" action="fup.cgi">
File to upload: <input type=file name=upfile><br>
Notes about the file: <input type=text name=note><br>
<input type=submit value=Press> to upload the file!
</form>
Not all browsers support form-based file upload, so try to give
alternatives where possible. Also, if you need to do file upload in
conjunction with form-to-email, the Perl package MIME::Lite handles
email attachments.
11.13. How can I use forms for pull-down navigation menus?
There is no way to do this in HTML only; something else must
process the form. JavaScript processing will work only for readers
with JavaScript-enabled browsers. CGI and other server-side
processing is reliable for human readers, but search engines have
problems following any form-based navigation.
See <http://www.cs.tut.fi/~jkorpela/forms/navmenu.html>, which
explains how to create pull-down menus, as well as some better
navigation alternatives.
Also, see item #3 of
<URL:http://www.useit.com/alertbox/990530.html>, which explains why
this might reduce the usability of your site.
Section 12: HTML Frames
12.1. How do I create frames? What is a frameset?
Frames allow an author to divide a browser window into multiple
(rectangular) regions. Multiple documents can be displayed in a
single window, each within its own frame. Graphical browsers allow
these frames to be scrolled independently of each other, and links
can update the document displayed in one frame without affecting
the others.
You can't just "add frames" to an existing document. Rather, you
must create a frameset document that defines a particular
combination of frames, and then display your content documents
inside those frames. The frameset document should also include
alternative non-framed content in a NOFRAMES element.
The HTML 4 frames model has significant design flaws that cause
usability problems for web users. Frames should be used only with
great care. The Web Design Group's guide to frames
<URL:http://www.htmlhelp.com/design/frames/> includes guidelines
on the suitable use of frames, in addition to a description of the
related HTML syntax.
12.2. How do I make a link or form in one frame update another frame?
In the frameset document (the HTML document containing the
<frameset> <frame> tags), make sure to name the individual frames
using the NAME attribute. The following example creates a top frame
named "navigation" and a bottom frame named "content":
<frameset rows="*,3*">
<frame name="navigation" src="navigation.html">
<frame name="content" src="content.html">
<noframes><body>
<!-- Alternative non-framed version -->
</body></noframes>
</frameset>
Then, in the document with the link, use the TARGET attribute to
specify which frame should be used to display the link. (The value
of the TARGET attribute should match the value of the target
frame's NAME attribute.) For example:
<a target="content" href=...>
To target a form submission, use the TARGET attribute of the FORM
element, like this:
<form target="content" action=...>
Note that when forms are processed entirely by JavaScript, the
target frame must be specified in the JavaScript. The value of the
TARGET attribute is irrelevant.
Normally, the default target frame is the current frame ("_self").
To change the default target for every link/form on the page, use
the TARGET attribute of the BASE element, like this:
<base target="content">
12.3. Why do my links open new windows rather than update an existing
frame?
If there is no existing frame with the name you used for the TARGET
attribute, then a new browser window will be opened, and this
window will be assigned the name you used. Furthermore,
TARGET="_blank" will open a new, unnamed browser window.
In HTML 4, the TARGET attribute value is case-insensitive, so that
abc and ABC both refer to the same frame/window, and _top and _TOP
both have the same meaning. However, most browsers treat the TARGET
attribute value as case-sensitive and do not recognize ABC as being
the same as abc, or _TOP as having the special meaning of _top.
Also, some browsers include a security feature that prevents
documents from being hijacked by third-party framesets. In these
browsers, if a document's link targets a frame defined by a
frameset document that is located on a different server than the
document itself, then the link opens in a new window instead.
12.4. How do I update two frames at once?
There are two basic techniques for updating multiple frames with a
single link: The HTML-based technique links to a new frameset
document that specifies the new combination of frames. The
JavaScript-based solution uses the onClick attribute of the link to
update the additional frame (or frames).
The HTML-based technique can link to a new frameset document with
the TARGET="_top" attribute (replacing the entire frameset).
However, there is an alternative if the frames to be updated are
part of a nested frameset. In the initial frameset document, use a
secondary frameset document to define the nested frameset. For
example:
<frameset cols="*,3*">
<frame src="contents.html" name="Contents">
<frame src="frameset2.html" name="Display">
<noframes><body>
<!-- Alternative non-framed version -->
</body></noframes>
</frameset>
A link can now use the TARGET="Display" attribute to replace
simultaneously all the frames defined by the frameset2.html
document.
The JavaScript-based solution uses the onClick attribute of the
link to perform the secondary update. For example:
<a href="URL1" target="Frame1"
onClick="top.Frame2.location='URL2';">Update frames</a>
The link will update Frame1 with URL1 normally. If the reader's
browser supports JavaScript (and has it enabled), then Frame2 will
also be updated (with URL2).
12.5. How do I get out of a frameset?
If you are the author, this is easy. You only have to add the
TARGET attribute to the link that takes readers to the intended
'outside' document. Give it the value of _top.
In many current browsers, it is not possible to display a frame in
the full browser window, at least not very easily. The reader would
need to copy the URL of the desired frame and then request that URL
manually.
I would recommend that authors who want to offer readers this
option add a link to the document itself in the document, with the
TARGET attribute set to _top so the document displays in the full
window if the link is followed.
12.6. How do I make sure my framed documents are displayed inside their
frameset?
When the sub-documents of a frameset state are accessed directly,
they appear without the context of the surrounding frameset.
If the reader's browser has JavaScript support enabled, the
following script will restore the frameset:
<SCRIPT TYPE="text/javascript">
<!--
if (parent.location.href == self.location.href) {
if (window.location.href.replace)
window.location.replace('frameset.html');
else
// causes problems with back button, but works
window.location.href = 'frameset.html';
}
// -->
</SCRIPT>
A more universal approach is a "restore frames" link:
<A HREF="frameset.html" TARGET="_top">Restore Frames</A>
Note that in either case, you must have a separate frameset
document for every content document. If you link to the default
frameset document, then your reader will get the default content
document, rather than the content document he/she was trying to
access. These frameset documents should be generated automatically,
to avoid the tedium and inaccuracy of creating them by hand.
Note that you can work around the problem with bookmarking frameset
states by linking to these separate frameset documents using
TARGET="_top", rather than linking to the individual content
documents.
12.7. Is there a way to prevent getting framed?
"Getting framed" refers to having your documents displayed within
someone else's frameset without your permission. This can happen
accidentally (the frameset author forgot to use TARGET="_top" when
linking to your document) or intentionally (the frameset author
wanted to display your content with his/her own navigation or
banner frames).
To avoid "framing" other people's documents, you must add
TARGET="_top" to all links that lead to documents outside your
intended scope.
Unfortunately, there is no reliable way to specify that a
particular document should be displayed in the full browser window,
rather than in the current frame. If you can configure your server
to send the proprietary header Window-Target: _top in the HTTP
response, then Netscape browsers will display your document in the
full browser window. However, other browsers ignore this header,
and it doesn't work to use <META HTTP-EQUIV="Window-target"
CONTENT="_top"> in the document itself to mimic the HTTP response.
Another workaround is to use <BASE TARGET="_top"> in the document,
but this only specifies the default target frame for links in the
current document, not for the document itself.
If the reader's browser has JavaScript enabled, the following
script will automatically remove any existing framesets:
<script type="text/javascript">
<!--
if (top.frames.length!=0) {
if (window.location.href.replace)
top.location.replace(self.location.href);
else
top.location.href=self.document.href;
}
// -->
</script>
An alternative script is
<script type="text/javascript">
<!--
function breakOut() {
if (self != top)
window.open("my URL","_top","");
}
// -->
</script>
</HEAD>
<BODY onLoad="breakOut()">
12.8. How do I specify a specific combination of frames instead of the
default document?
This is unfortunately not possible. When you navigate through a
site using frames, the URL will not change as the documents in the
individual frames change. This means that there is no way to
indicate the combination of documents that make up the current
state of the frameset.
The author can provide multiple frameset documents, one for each
combination of frame content. These frameset documents can be
generated automatically, perhaps being created on the fly by a CGI
program. Rather than linking to individual content documents, the
author can link to these separate frameset documents using
TARGET="_top". Thus, the URL of the current frameset document will
always specify the combination of frames being displayed, which
allows links, bookmarks, etc. to function normally.
12.9. How do I remove the border around frames?
Removing the border around frames involves both not drawing the
frame borders and eliminating the space between the frames. The two
major frames-capable browsers use different proprietary attributes
to achieve this.
Netscape recognizes the BORDER attribute on FRAMESET. It can be set
to 0, in which case the border will not be shown, and the spacing
will be set to zero.
Microsoft Internet Explorer recognizes the FRAMEBORDER and
FRAMESPACING attributes on FRAMESET, but in some versions also on
FRAME for individual frames. Both attributes must be set to 0.
So, the most widely supported way to display borderless frames is
<FRAMESET ... BORDER=0 FRAMEBORDER=0 FRAMESPACING=0>.
Note that these attributes are proprietary and not part of the HTML
4 specifications. Also, removing the border around a frame makes it
impossible to resize it, as this border is also used in most GUIs
to change the size of the window.
12.10. How do I make a frame with a vertical scrollbar but without a
horizontal scrollbar?
The only way to have a frame with a vertical scrollbar but without
a horizontal scrollbar is to define the frame with SCROLLING="auto"
(the default), and to have content that does not require horizontal
scrolling. There is no way to specify that a frame should have one
scrollbar but not the other. Using SCROLLING="yes" will force
scrollbars in both directions (even when they aren't needed), and
using SCROLLING="no" will inhibit all scrollbars (even when
scrolling is necessary to access the frame's content). There are no
other values for the SCROLLING attribute.
12.11. How do I change the title of a framed document?
The title displayed is the title of the frameset document rather
than the titles of any of the pages within frames. To change the
title displayed, link to a new frameset document using
TARGET="_top" (replacing the entire frameset).
12.12. Why aren't my frames the exact size I specified?
Netscape Navigator seems to convert pixel-based frame dimensions to
whole percentages, and to use those percentage-based dimensions
when laying out the frames. Thus, frames with pixel-based
dimensions will be rendered with a slightly different size than
that specified in the frameset document. The rounding error will
vary depending on the exact size of the browser window.
Furthermore, Navigator seems to store the percentage-based
dimensions internally, rather than the original pixel-based
dimensions. Thus, when a window is resized, the frames are redrawn
based on the new window size and the old percentage-based
dimensions.
There is no way to prevent this behavior. To accomodate it, you
should design your site to adapt to variations in the frame
dimensions. This is another situation where it is a good idea to
accomodate variations in the browser's presentation.
12.13. Are there any problems with using frames?
The fundamental problem with the design of frames is that framesets
create states in the browser that are not addressable. Once any of
the frames within a frameset changes from its default content,
there is no longer a way to address the current state of the
frameset. It is difficult to bookmark - and impossible to link or
index - such a frameset state. It is impossible to reference such a
frameset state in other media. When the sub-documents of such a
frameset state are accessed directly, they appear without the
context of the surrounding frameset. Basic browser functions (e.g.,
printing, moving forwards/backwards in the browser's history)
behave differently with framesets. Also, browsers cannot identify
which frame should have focus, which affects scrolling, searching,
and the use of keyboard shortcuts in general.
Furthermore, frames focus on layout rather than on information
structure, and many authors of framed sites neglect to provide
useful alternative content in the NOFRAMES element. Both of these
factors cause accessibility problems for browsers that differ
significantly from the author's expectations and for search
engines.
For further discussion, see
<URL:http://www.htmlhelp.com/design/frames/whatswrong.html>
For better alternatives to common uses of frames, see the answers
to the questions "How do I include one file in another?" and "How
do I put links along the left side of my page?"
12.14. Do search engines dislike frames?
Search engines can link directly to framed content documents, but
they cannot link to the combinations of frames for which those
content documents were designed. This is the result of a
fundamental flaw in the design of frames.
Search engines try to provide their users with links to useful
documents. Many framed content documents are difficult to use when
accessed directly (outside their intended frameset), so there is
little benefit if search engines offer links to them. Therefore,
many search engines ignore frames completely and go about indexing
more useful (non-framed) documents.
Search engines will index your <NOFRAMES> content, and any content
that is accessible via your <NOFRAMES> content. Such content should
be useful when accessed directly from a search-engine link.
------------------------------------------------------------
Copyright ╘ 1996-2001 by the Web Design Group. This material may be
distributed only subject to the terms and conditions set forth in
the Open Publication License, v1.0 or later (the latest version is
presently available at http://www.opencontent.org/openpub/).
--
Darin McGrew, [email protected], http://www.rahul.net/mcgrew/
Web Design Group, [email protected], http://www.HTMLHelp.com/
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