上海时时乐上

上海时时乐群:HTML Techniques for Web Content Accessibility Guidelines 1.0

W3C Note 6 November 2000

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Editors:
Wendy Chisholm, 上海时时乐上;
Gregg Vanderheiden, Trace R & D Center University of Wisconsin -- Madison;
Ian Jacobs, 上海时时乐上

Abstract

This document describes techniques for authoring accessible Hypertext Markup Language (HTML) content (refer to HTML 4.01 [HTML4]). This document is intended to help authors of Web content who wish to claim conformance to "Web Content Accessibility Guidelines 1.0" ([WCAG10]). While the techniques in this document should help people author HTML that conforms to "Web Content Accessibility Guidelines 1.0", these techniques are neither guarantees of conformance nor the only way an author might produce conforming content.

This document is part of a series of documents about techniques for authoring accessible Web content. For information about the other documents in the series, please refer to "Techniques for Web Content Accessibility Guidelines 1.0" [WCAG10-TECHS].

Note: This document contains a number of examples that illustrate accessible solutions in CSS but also deprecated examples that illustrate what content developers should not do. The deprecated examples are highlighted and readers should approach them with caution -- they are meant for illustrative purposes only.

Status of this document

This version has been published to correct some broken links in the previous version.

The 6 November 2000 version of this document is a Note in a series of Notes produced and endorsed by the Web Content Accessibility Guidelines Working Group (WCAG WG). This Note has not been reviewed or endorsed by W3C Members. The series of documents supersedes the single document 5 May 1999 W3C Note Techniques for Web Content Accessibility Guidelines 1.0. The topics from the earlier document have been separated into technology-specific documents that may evolve independently. Smaller technology-specific documents allow authors to focus on a particular technology.

While the "Web Content Accessibility Guidelines 1.0" Recommendation [WCAG10] is a stable document, this series of companion documents is expected to evolve as technologies change and content developers discover more effective techniques for designing accessible Web content.

The history of changes to the series of documents as well as the list of open and closed issues are available. Readers are encouraged to comment on the document and propose resolutions to current issues. Please send detailed comments on this document to the Working Group at [email protected]; public archives are available.

The English version of this specification is the only normative version. Translations of this document may be available.

The list of known errors in this document is available at "Errata in Web Content Accessibility Guidelines." Please report errors in this document to [email protected].

The Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C) makes available a variety of resources on Web accessibility. WAI Accessibility Guidelines are produced as part of the WAI Technical Activity. The goals of the Web Content Accessibility Guidelines Working Group are described in the charter.

A list of current W3C Recommendations and other technical documents is available.

Table of Contents


1 Document structure and metadata

Content developers should use structural markup and use it according to specification. Structural elements and attribute (refer to the index of HTML elements and attributes to identify them) promote consistency in documents and supply information to other tools (e.g., indexing tools, search engines, programs that extract tables to databases, navigation tools that use heading elements, and automatic translation software that translates text from one language into another.

1.1 Metadata

Checkpoints in this section:

Some structural elements provide information about the document itself. This is called "metadata" about the document -- metadata is information about data. Well-crafted metadata can provide important orientation information to users. HTML elements that provide useful information about a document include:

1.1.1 TITLE: The document title.

Note that the (mandatory) TITLE element, which only appears once in a document, is different from the "title" attribute, which applies to almost every HTML 4.01 element. Content developers should use the "title" attribute in accordance with the HTML 4.01 specification. For example, "title" should be used with links to provide information about the target of the link.

1.1.2 The ADDRESS element

This element can be used to provide information about the creator of the page.

1.1.3 The META element

Checkpoints in this section:

This element can specify metadata for a document including keywords, and information about the author. Please refer to the section on automatic page refresh for information on why META should not be used to redirect or auto-refresh pages.

The following are deprecated HTML examples. The first changes the user's page at page at regular intervals. Content developers should not use this technique to simulate "push" technology. Developers cannot predict how much time a user will require to read a page; premature refresh can disorient users. Content developers should avoid periodic refresh and allow users to choose when they want the latest information.

Deprecated example.

<META http-equiv="refresh" content="60">
<BODY>
<P>...Information...
</BODY>

End example.

The following HTML example (using the META element) forwards the user from one page to another after a timeout. However, users should not redirect users with this markup since is non-standard, it disorients users, and it can disrupt a browser's history of visited pages.

Deprecated example.

<HEAD>
<TITLE>Don't use this!</TITLE>
<META http-equiv="refresh" content="5;
         //www.example.com/newpage">
</HEAD>
<BODY>
<P>If your browser supports Refresh,
you'll be transported to our
<A >new site</A>
in 5 seconds, otherwise, select the link manually.
</BODY>

End example.

1.1.4 The !DOCTYPE statement

Checkpoints in this section:

Validating to a published formal grammar and declaring that validation at the beginning of a document lets the user know that the structure of the document is sound. It also lets the user agent know where to look for semantics if it needs to. The W3C Validation Service validates documents against a whole list of published grammars.

It is preferable to validate to W3C grammars. Refer to the Technologies Reviewed for Accessibility.

1.1.5 The LINK element and navigation tools

Checkpoints in this section:

Content developers should use the LINK element and link types (refer to [HTML4], section 6.12) to describe document navigation mechanisms and organization. Some user agents may synthesize navigation tools or allow ordered printing of a set of documents based on such markup.

Example.

The following LINK elements might be included in the head of chapter 2 of a book:

   <LINK rel="Next" href="chapter3">
   <LINK rel="Prev" href="chapter1">
   <LINK rel="Start" href="cover">
   <LINK rel="Glossary" href="glossary">

End example.

1.1.6 The LINK element and alternative documents

Checkpoints in this section:

The LINK element may also be used to designate alternative documents. Browsers should load the alternative page automatically based on the user's browser type and preferences. For example, use the LINK element as follows:

Example.

User agents that support LINK will load the alternative page for those users whose browsers may be identified as supporting "aural","braille", or "tty" rendering.

        <HEAD>
        <TITLE>Welcome to the Virtual Mall!</TITLE>
        <LINK title="Text-only version"
              rel="alternate"
              href="text_only"
              media="aural, braille, tty">
        </HEAD>
        <BODY><P>...</BODY>

End example.

1.2 Structural grouping

Checkpoints in this section:

The following HTML 4.01 mechanisms group content and make it easier to understand.:

All of these grouping mechanisms should be used when appropriate and natural, i.e., when the information lends itself to logical groups. Content developers should not create groups randomly, as this will confuse all users.

1.2.1 Section headings

Checkpoints in this section:

Long documents are often divided into a variety of chapters, chapters have subtopics and subtopics are divided into various sections, sections into paragraphs, etc. These semantic chunks of information make up the structure of the document.

Sections should be introduced with the HTML heading elements (H1-H6). Other markup may complement these elements to improve presentation (e.g., the HR element to create a horizontal dividing line), but visual presentation is not sufficient to identify document sections.

Since some users skim through a document by navigating its headings, it is important to use them appropriately to convey document structure. Users should order heading elements properly. For example, in HTML, H2 elements should follow H1 elements, H3 elements should follow H2 elements, etc. Content developers should not "skip" levels (e.g., H1 directly to H3). Do not use headings to create font effects; use style sheets to change font styles for example.

Note that in HTML, heading elements (H1 - H6) only start sections, they don't contain them as element content. The following HTML markup shows how style sheets may be used to control the appearance of a heading and the content that follows:

Example.

   <HEAD>
   <TITLE>Cooking techniques</TITLE>
   <STYLE type="text/css">
      /* Indent heading and following content */
      DIV.section2 { margin-left: 5% }
   </STYLE>
   </HEAD>
   <BODY>
   <H1>Cooking techniques</H1>
   ... some text here ...
   <DIV class="section2">
   <H2>Cooking with oil</H2>
   ... text of the section ...
   </DIV>

   <DIV class="section2">
   <H2>Cooking with butter</H2>
   ... text of the section ...
   </DIV>

End example.

See also the section on links.

2 Language information

2.1 Identifying changes in language

Checkpoints in this section:

If you use a number of different languages on a page, make sure that any changes in language are clearly identified by using the "lang" attribute:

Example.

   <P>And with a certain <SPAN lang="fr">je ne sais quoi</SPAN>, 
   she entered both the room, and his life, forever. <Q>My name
   is Natasha,</Q> she said. <Q lang="it">Piacere,</Q>
   he replied in impeccable Italian, locking the door.

End example.

Identifying changes in language are important for a number of reasons:

  1. Users who are reading the document in braille will be able to substitute the appropriate control codes (markup) where language changes occur to ensure that the braille translation software will generate the correct characters (accented characters, for instance). These control codes also prevent braille contractions from being generated, which could further confuse the user. Braille contractions combine commonly used groups of characters that usually appear in multiple cells into a single cell. For example, "ing" which usually takes up three cells (one for each character) can be contracted into a single cell.
  2. Similarly, speech synthesizers that "speak" multiple languages will be able to generate the text in the appropriate accent with proper pronunciation. If changes are not marked, the synthesizer will try its best to speak the words in the primary language it works in. Thus, the French word for car, "voiture" would be pronounced "voter" by a speech synthesizer that uses English as its primary language.
  3. Users who are unable to translate between languages themselves, will be able to have unfamiliar languages translated by machine translators.

2.2 Identifying the primary language

Checkpoints in this section:

It is also good practice to identify the primary language of a document, either with markup (as shown below) or through HTTP headers.

Example.

    <HTML lang="fr">
       ....rest of an HTML document written in French...
    </HTML>

End example.

3 Text markup

The following sections discuss ways to add structure to pieces of text.

3.1 Emphasis

Checkpoints in this section:

The proper HTML elements should be used to mark up emphasis: EM and STRONG. The B and I elements should not be used; they are used to create a visual presentation effect. The EM and STRONG elements were designed to indicate structural emphasis that may be rendered in a variety of ways (font style changes, speech inflection changes, etc.)

3.2 Acronyms and abbreviations

Checkpoints in this section:

Mark up abbreviations and acronyms with ABBR and ACRONYM and use "title" to indicate the expansion:

Example.

   <P>Welcome to the <ACRONYM title="World Wide Web">WWW</ACRONYM>!

End example.

This also applies to shortened phrases used as headings for table row or columns. If a heading is already abbreviated provide the expansion in ABBR. If a heading is long, you may wish to provide an abbreviation, as described in Data Tables.

Example.

  ...
  <TH>First name</TH>
  <TH><ABBR title="Social Security Number">SS#</ABBR>
  ...

End example.

3.3 Quotations

Checkpoints in this section:

The Q and BLOCKQUOTE elements mark up inline and block quotations, respectively.

Example.

This example marks up a longer quotation with BLOCKQUOTE:

   <BLOCKQUOTE cite="//www.example.com/loveslabourlost">
     <P>Remuneration! O! that's the Latin word for three farthings.
        --- William Shakespeare (Love's Labor Lost).
     </P>
   </BLOCKQUOTE>

End example.

3.4 Markup and style sheets rather than images: The example of math

Checkpoints in this section:

Using markup (and style sheets) where possible rather than images (e.g., a mathematical equation) promotes accessibility for the following reasons:

As an example, consider these techniques for putting mathematics on the Web:

TeX is commonly used to create technical papers which are then converted to HTML for publication on the Web. However, converters tend to generate images, use deprecated markup, and use tables for layout. Consequently, content providers should:

  1. Make the original TeX (or LaTeX) document available on the Web. There is a system called "AsTeR" ([ASTER]) that can create an auditory rendition of TeX and LaTeX documents. Also, IBM has a plug-in for Netscape and Internet Explorer that reads TeX/LaTeX documents and some of MathML (refer to [HYPERMEDIA]). Note. These tools work primarily in the English environment and may not work so well with speech synthesizers whose primary language is not English.
  2. Ensure that the HTML created by the conversion process is accessible. Provide a single description of the equation (rather than "alt" text on every generated image as there may be small images for bits and pieces of the equation).

3.5 Eight other structural elements (to identify citations, code fragments, deleted text, and others)

The HTML 4.01 specification defines the following structural elements for miscellaneous markup needs:

CITE
Contains a citation or a reference to other sources.
DFN
Indicates that this is the defining instance of the enclosed term.
CODE
Designates a fragment of computer code.
SAMP
Designates sample output from programs, scripts, etc.
KBD
Indicates text to be entered by the user.
VAR
Indicates an instance of a variable or program argument.
INS
Indicates text inserted into a document.
DEL
Indicates text deleted from a document.

4 Lists

Checkpoints in this section:

The HTML list elements DL, UL, and OL should only be used to create lists, not for formatting effects such as indentation. Refer to information on CSS and tables for layout in the CSS Techniques [WCAG10-CSS-TECHNIQUES].

Ordered lists help non-visual users navigate. Non-visual users may "get lost" in lists, especially in nested lists and those that do not indicate the specific nest level for each list item. Until user agents provide a means to identify list context clearly (e.g., by supporting the ':before' pseudo-element in CSS2), content developers should include contextual clues in their lists.

For numbered lists, compound numbers are more informative than simple numbers. Thus, a list numbered "1, 1.1, 1.2, 1.2.1, 1.3, 2, 2.1," provides more context than the same list without compound numbers, which might be formatted as follows:

1.
  1.
  2.
    1.
  3.
2.
  1.

and would be spoken as "1, 1, 2, 1, 2, 3, 2, 1", conveying no information about list depth.

[CSS1] and [CSS2] allow users to control number styles (for all lists, not just ordered) through user style sheets.

Example.

The following CSS2 style sheet shows how to specify compound numbers for nested lists created with either UL or OL elements. Items are numbered as "1", "1.1", "1.1.1", etc.

<STYLE type="text/css">
   UL, OL { counter-reset: item }
   LI { display: block }
   LI:before { content: counters(item, "."); counter-increment: item }
</STYLE>

End example.

Until either CSS2 is widely supported or user agents allow users to control rendering of lists through other means, authors should consider providing contextual clues in unnumbered nested lists. Non-visual users may have difficulties knowing where a list begins and ends and where each list item starts. For example, if a list entry wraps to the next line on the screen, it may appear to be two separate items in the list. This may pose a problem for legacy screen readers.

4.1 Use style sheets to change list bullets

To change the "bullet" style of unordered list items created with the LI element, use style sheets. In CSS, it is possible to specify a fallback bullet style (e.g., 'disc') if a bullet image cannot be loaded.

Example.

<HEAD>
<TITLE>Using style sheets to change bullets</TITLE>
<STYLE type="text/css">
   UL { list-style: url(star.gif) disc }
</STYLE>
</HEAD>
<BODY>
<UL>
   <LI>Audrey
   <LI>Laurie
   <LI>Alice
</UL>

End example.

To further ensure that users understand differences between list items indicated visually, content developers should provide a text label before or after the list item phrase:

Example.

In this example, new information is communicated through text ("New"), font style (bold), and color (yellow bullet, red text on yellow background).

<HEAD>
<TITLE>Bullet styles example</TITLE>
<STYLE type="text/css">
   .newtxt { font-weight: bold;
             color: red;
             background-color: yellow }
   .newbullet { list-style : url(yellow.gif) disc }
</STYLE>
</HEAD>
<BODY>
<UL>
   <LI class="newbullet">Roth IRA <SPAN class="newtext">New</SPAN></LI>
   <LI> 401(k)</LI>
</UL>
</BODY>

End example.

4.1.1 Images used as bullets

Checkpoints in this section:

Avoid using images as bullets in definition lists created with DL, DT, and DD. However, if this method is used, be sure to provide a text equivalent for the images.

Deprecated example.

<HEAD>
<TITLE>Deprecated example using image in DL lists</TITLE>
</HEAD>
<BODY>
<DL>
   <DD><IMG src="star.gif" alt="* ">Audrey
   <DD><IMG src="star.gif" alt="* ">Laurie
   <DD><IMG src="star.gif" alt="* ">Alice
</DL>

End example.

Content developers should avoid list styles where bullets provide additional (visual) information. However, if this is done, be sure to provide a text equivalent describing meaning of the bullet:

Deprecated example.

<DL>
<DD><IMG src="red.gif" alt="New:">Roth IRA</DD>
<DD><IMG src="yellow.gif" alt="Old:">401(k)</DD>
</DL>

End example.

5 Tables

This section discusses the accessibility of tables and elements that one can put in a TABLE element. Two types of tables are discussed: tables used to organize data, and tables used to create a visual layout of the page.

5.1 Tables of data

Content developers may make HTML 4.01 data tables more accessible in a number of ways:

5.1.1 Providing summary information

Checkpoints in this section:

5.1.2 Identifying rows and column information

Checkpoints in this section:

Example.

This example shows how to associate data cells (created with TD) with their corresponding headers by means of the "headers" attribute. The "headers" attribute specifies a list of header cells (row and column labels) associated with the current data cell. This requires each header cell to have an "id" attribute.

   <TABLE border="1" 
          summary="This table charts the number of
                   cups of coffee consumed by each senator,  
                   the type of coffee (decaf or regular),
                   and whether taken with sugar.">
     <CAPTION>Cups of coffee consumed by each senator</CAPTION>
     <TR>   
         <TH id="header1">Name</TH>
         <TH id="header2">Cups</TH>     
         <TH id="header3" abbr="Type">Type of  Coffee</TH>   
         <TH id="header4">Sugar?</TH>
     <TR>  
         <TD headers="header1">T. Sexton</TD>  
         <TD headers="header2">10</TD>
         <TD headers="header3">Espresso</TD>
         <TD headers="header4">No</TD>  
     <TR>  
         <TD headers="header1">J. Dinnen</TD> 
         <TD headers="header2">5</TD>
         <TD headers="header3">Decaf</TD>
        <TD headers="header4">Yes</TD>
  </TABLE>

End example.

A speech synthesizer might render this tables as follows:

  Caption: Cups of coffee consumed by each senator
  Summary: This table charts the number of cups of coffee
           consumed by each senator, the type of coffee
          (decaf or regular), and whether taken with sugar.
  Name: T. Sexton, Cups: 10, Type: Espresso, Sugar: No
  Name: J. Dinnen, Cups: 5, Type: Decaf, Sugar: Yes

A visual user agent might render this table as follows:

Illustration of coffee table rendering [Description of coffee table]

The next example associates the same header (TH) and data (TD) cells as before, but this time uses the "scope" attribute rather than "headers". "Scope" must have one of the following values: "row", "col", "rowgroup", or "colgroup." Scope specifies the set of data cells to be associated with the current header cell. This method is particularly useful for simple tables. It should be noted that the spoken rendering of this table would be identical to that of the previous example. A choice between the "headers" and "scope" attributes is dependent on the complexity of the table. It does not affect the output so long as the relationships between header and data cells are made clear in the markup.

Example.

   <TABLE border="1" 
          summary="This table charts ...">  
      <CAPTION>Cups of coffee consumed by each senator</CAPTION>
      <TR>  
           <TH scope="col">Name</TH>
           <TH scope="col">Cups</TH>
           <TH scope="col" abbr="Type">Type of Coffee</TH>  
           <TH scope="col">Sugar?</TH>
     <TR>  
           <TD>T. Sexton</TD>  <TD>10</TD>
           <TD>Espresso</TD>   <TD>No</TD>
     <TR>  
           <TD>J. Dinnen</TD>  <TD>5</TD>
           <TD>Decaf</TD>       <TD>Yes</TD>
  </TABLE>

End example.

The following example shows how to create categories within a table using the "axis" attribute.

Example.

   <TABLE border="1">
     <CAPTION>Travel Expense Report</CAPTION>
     <TR>  
          <TH></TH>  
          <TH id="header2" axis="expenses">Meals
          <TH id="header3" axis="expenses">Hotels
          <TH id="header4" axis="expenses">Transport
          <TD>subtotals</TD>    
     <TR>  
          <TH id="header6" axis="location">San Jose
          <TH> <TH> <TH> <TD> 
     <TR>  
         <TD id="header7" axis="date">25-Aug-97
         <TD headers="header6 header7 header2">37.74
         <TD headers="header6 header7 header3">112.00
         <TD headers="header6 header7 header4">45.00
         <TD>
     <TR>  
         <TD id="header8" axis="date">26-Aug-97
         <TD headers="header6 header8 header2">27.28
         <TD headers="header6 header8 header3">112.00
         <TD headers="header6 header8 header4">45.00 
         <TD>
     <TR>  
         <TD>subtotals 
         <TD>65.02
         <TD>224.00
         <TD>90.00
         <TD>379.02
     <TR>   
         <TH id="header10" axis="location">Seattle
         <TH> <TH> <TH> <TD>
     <TR>  
         <TD id="header11" axis="date">27-Aug-97
         <TD headers="header10 header11 header2">96.25
         <TD headers="header10 header11 header3">109.00
         <TD headers="header10 header11 header4">36.00
         <TD>
     <TR>  
         <TD id="header12" axis="date">28-Aug-97
         <TD headers="header10 header12 header2">35.00
         <TD headers="header10 header12 header3">109.00
         <TD headers="header10 header12 header4">36.00 
         <TD>
     <TR>  
         <TD>subtotals
         <TD>131.25
         <TD>218.00
         <TD>72.00
         <TD>421.25
     <TR>   
         <TH>Totals
         <TD>196.27
         <TD>442.00
         <TD>162.00
         <TD>800.27
   </TABLE>

End example.

This table lists travel expenses at two locations: San Jose and Seattle, by date, and category (meals, hotels, and transport). The following image shows how a visual user agent might render it. [Description of travel table]

Travel Expense Report table as rendered by a visual user agent.

5.2 Tables for layout

Checkpoints in this section:

Authors should use style sheets for layout and positioning. However, when it is necessary to use a table for layout, the table must linearize in a readable order. When a table is linearized, the contents of the cells become a series of paragraphs (e.g., down the page) one after another. Cells should make sense when read in row order and should include structural elements (that create paragraphs, headings, lists, etc.) so the page makes sense after linearization.

Also, when using tables to create a layout, do not use structural markup to create visual formatting. For example, the TH (table header) element, is usually displayed visually as centered, and bold. If a cell is not actually a header for a row or column of data, use style sheets or formatting attributes of the element.

5.3 Linearizing tables

Checkpoints in this section:

Tables used to lay out pages where cell text wraps pose problems for older screen readers that do not interpret the source HTML or browsers that do not allow navigation of individual table cells. These screen readers will read across the page, reading sentences on the same row from different columns as one sentence.

For example, if a table is rendered like this on the screen:

There is a 30% chance of               Classes at the University of Wisconsin 
rain showers this morning, but they    will resume on September 3rd. 
should stop before the weekend.

This might be read by a screen reader as:

There is a 30% chance of Classes at the University of Wisconsin
rain showers this morning, but they will resume on September 3rd. 
should stop before the weekend.

It is usually very simple to linearize a table used to layout a page - simply strip the table markup from the table. There are several tools that do this, and it is becoming more common for screen readers and some browsers to linearize tables.

However, linearizing data tables requires a different strategy. Since data cells rely on the information provided by surrounding and header cells, the relationship information that is available visually needs to be translated into the linear table.

For example, specify the column layout order. The natural language writing direction may affect column layout and thus the order of a linearized table. The "dir" attribute specifies column layout order (e.g., dir="rtl" specifies right-to-left layout).

This markup will also help browsers linearize tables (also called table "serialization"). A row-based linear version may be created by reading the row header, then preceding each cell with the cell's column header. Or, the linearization might be column-based. Future browsers and assistive technologies will be able to automatically translate tables into linear sequences or navigate a table cell by cell if data is labeled appropriately. The WAI Evaluation and Repair working group is tracking the progress of tools as well as developing their own that will allow users to linearize or navigate tables cell by cell. Refer to [WAI-ER].

Quicktest! To get a better understanding of how a screen reader would read a table, run a piece of paper down the page and read your table line by line.

5.4 Backward compatibility issues for tables

In HTML 3.2 browsers, the rows of a TFOOT element will appear before the table body.

6 Links

6.1 Link text

Checkpoints in this section:

Good link text should not be overly general; don't use "click here." Not only is this phrase device-dependent (it implies a pointing device) it says nothing about what is to be found if the link if followed. Instead of "click here", link text should indicate the nature of the link target, as in "more information about sea lions" or "text-only version of this page". Note that for the latter case (and other format- or language-specific documents), content developers are encouraged to use content negotiation instead, so that users who prefer text versions will have them served automatically.

In addition to clear link text, content developers may specify a value of the "title" attribute that clearly and accurately describes the target of the link.

If more than one link on a page shares the same link text, all those links should point to the same resource. Such consistency will help page design as well as accessibility.

If two or more links refer to different targets but share the same link text, distinguish the links by specifying a different value for the "title" attribute of each A element.

"Auditory users" -- people who are blind, have difficulty seeing, or who are using devices with small or no displays -- are unable to scan the page quickly with their eyes. To get an overview of a page or to quickly find a link, these users will often tab from one link to the next or review a list of available links on a page.

Thus, for a series of related links, include introductory information in the first link, then distinguishing information in the links that follow. This will provide context information for users reading them in sequence.

Example.

  <A href="my-doc.html">My document is available in HTML</A>,
  <A href="my-doc.pdf" title="My document in PDF">PDF</A>,
  <A href="my-doc.txt" title="My document in text">plain text</A>

End example.

6.1.1 Text for images used as links

Checkpoints in this section:

When an image is used as the content of a link, specify a text equivalent for the image.

Example.

  <A href="routes.html">
     <IMG src="topo.html" 
          alt="Current routes at Boulders Climbing Gym">
  </A>

End example.

Or, if you provide link text, use a space as the "alt" attribute value of the IMG element. Note that this text will appear on the page next to the image.

Example.

  <A href="routes.html">
     <IMG src="topo.html" alt=" ">
        Current routes at Boulders Climbing Gym
  </A>

End example.

6.2 Grouping and bypassing links

Checkpoints in this section:

When links are grouped into logical sets (for example, in a navigation bar that appears on every page in a site) they should be marked up as a unit. Navigation bars are usually the first thing someone encounters on a page. For users with speech synthesizers, this means having to hear a number of links on every page before reaching the interesting content of a page. There are several ways to allow users to bypass groups of links (as users with vision do when they see the same set on each page):

In the future, user agents may allow users to skip over elements such as navigation bars.

Example.

In this example, the MAP element groups a set of links, the "title" attribute identifies it as a navigation bar , and a link at the beginning of the group links to the anchor after the group. Also, note that the links are separated by non-link, printable characters (surrounded by spaces).

   <BODY>     
     <MAP title="Navigation Bar">    
       <P>
       [<A href="#how">Bypass navigation bar</A>]
       [<A href="home.html">Home</A>]
       [<A href="search.html">Search</A>]
       [<A href="new.html">New and highlighted</A>]
       [<A href="sitemap.html">Site map</A>]
       </P>
     </MAP>     
     <H1><A name="how">How to use our site</A></H1>
   <!-- content of page -->     
   </BODY>     

End example.

6.3 Keyboard access

Checkpoints in this section:

Keyboard access to active elements of a page is important for many users who cannot use a pointing device. User agents may include features that allow users to bind keyboard strokes to certain actions. HTML 4.01 allows content developers to specify keyboard shortcuts in documents via the "accesskey" attribute.

Example.

In this example, if the user activates the "C" key, the link will be followed.

   <A accesskey="C" href="doc.html" hreflang="en"
      title="XYZ company home page">
         XYZ company home page</A>

End example.

Note: Until user agents provide an overview of which key bindings are available, provide information on the key bindings.

6.4 Anchors and targets

Checkpoints in this section:

7 Images and image maps

The following sections discuss accessibility of images (including simple animations such as GIF animations) and image maps.

For information about math represented as images, refer to the section on using text markup and style sheets rather than images.

7.1 Short text equivalents for images ("alt-text")

Checkpoints in this section:

When using IMG, specify a short text equivalent with the "alt" attribute. Note. The value of this attribute is referred to as "alt-text".

Example.

   <IMG src="magnifyingglass.gif" alt="Search">     

End example.

When using OBJECT, specify a text equivalent in the body of the OBJECT element:

Example.

   <OBJECT data="magnifyingglass.gif" type="image/gif">
      Search 
   </OBJECT>

End example.

7.2 Long descriptions of images

Checkpoints in this section:

When a short text equivalent does not suffice to adequately convey the function or role of an image, provide additional information in a file designated by the "longdesc" attribute:

Example.

   <IMG src="97sales.gif" alt="Sales for 1997" 
        longdesc="sales97.html">

In sales97.html:

A chart showing how sales in 1997 progressed. The chart
is a bar-chart showing percentage increases in sales
by month. Sales in January were up 10% from December 1996,
sales in February dropped 3%, ..

End example.

For user agents that don't support "longdesc", provide a description link as well next to the graphic:

Example.

   <IMG src="97sales.gif" alt="Sales for 1997" longdesc="sales.html">
   <A href="sales.html" title="Description of 1997 sales figures">[D]</A>

End example.

When using OBJECT, specify longer text equivalent within the element's content:

Example.

   <OBJECT data="97sales.gif" type="image/gif">
          Sales in 1997 were down subsequent to our
          <A href="anticipated.html">anticipated 
          purchase</A> ...
   </OBJECT>

End example.

Note that OBJECT content, unlike "alt" text, can include markup. Thus, content developers can provide a link to additional information from within the OBJECT element:

Example.

   <OBJECT data="97sales.gif" type="image/gif">
          Chart of our Sales in 1997.
          A <A href="desc.html">textual description</A> is available. 
  </OBJECT>

End example.

7.2.1 Invisible d-links

Note. Invisible d-links are deprecated in favor of the "longdesc" attribute.

An invisible d-link is a small (1-pixel) or transparent image whose "alt" attribute value is "D-link" or "D" and is part of the content of an A element. Like other d-links, it refers to a text equivalent of the associated image. Like other links, users can tab to it. Invisible d-links thus provide a (temporary) solution for designers who wish to avoid visible d-links for stylistic reasons.

7.3 Ascii art

Checkpoints in this section:

Avoid ASCII art (character illustrations) and use real images instead since it is easier to supply a text equivalent for images. However, if ASCII art must be used provide a link to jump over the ASCII art, as follows.

Example.

<P>
<a href="#post-art">skip over ASCII art</a>
<!-- ASCII art goes here -->
<a name="post-art">caption for ASCII art</a>

End example.

ASCII art may also be marked up as follows [skip over ASCII figure or consult a description of chart]:

Example.

 
  %   __ __ __ __ __ __ __ __ __ __ __ __ __ __   
100 |             *                             |
 90 |                *  *                       |
 80 |          *           *                    |
 70 |             @           *                 |
 60 |          @                 *              |
 50 |       *        @              *           |
 40 |                   @              *        |
 30 |    *  @              @  @           *     |
 20 |                                           |
 10 |    @                       @  @  @  @     |
      0  5 10 15 20 25 30 35 40 45 50 55 60 65 70
      Flash frequency (Hz)

End example.

Another option for smaller ascii art is to use an ABBR element with "title".

Example.

<P><ABBR title="smiley in ASCII art">:-)</ABBR>

End example.

If the ASCII art is complex, ensure that the text equivalent adequately describes it.

Another way to replace ASCII art is to use human language substitutes. For example, <wink> might substitute for a winking smiley: ;-). Or, the word "therefore" can replace arrows consisting of dashes and greater than signs (e.g., -->), and the word "great" for the uncommon abbreviation "gr8".

7.4 Image maps

An image map is an image that has "active regions". When the user selects one of the regions, some action takes place -- a link may be followed, information may be sent to a server, etc. To make an image map accessible, content developers must ensure that each action associated with a visual region may be activated without a pointing device.

Image maps are created with the MAP element. HTML allows two types of image maps: client-side (the user's browser processes a URI) and server-side (the server processes click coordinates). For all image maps, content developers must supply a text equivalent.

Content developers should create client-side image maps (with "usemap") rather than server-side image maps (with "ismap") because server-side image maps require a specific input device. If server-side image maps must be used (e.g., because the geometry of a region cannot be represented with values of the shape attribute), authors must provide the same functionality or information in an alternative accessible format. One way to achieve this is to provide a textual link for each active region so that each link is navigable with the keyboard. If you must use a server-side image map, please consult the section on server-side image maps

7.4.1 Text equivalents for client-side image maps

Checkpoints in this section:

Provide text equivalents for image maps since they convey visual information. As with other links, the link text should make sense when read out of context. Refer to the section on Link Text for information on writing good link text. Users may also want keyboard shortcuts to access frequently followed links. Refer to the section on Keyboard access to links.

If AREA is used to create the map, use the "alt" attribute:

Example.

   <IMG src="welcome.gif" alt="Image map of areas in the library"
        usemap="#map1">
   <MAP name="map1">
     <AREA shape="rect" coords="0,0,30,30"
           href="reference.html" alt="Reference">
     <AREA shape="rect" coords="34,34,100,100"
           href="media.html" alt="Audio visual lab">
   </MAP>

End example.

The following example illustrates the same idea, but uses OBJECT instead of IMG to insert the image to provide more information about the image:

Example.

   <OBJECT data="welcome.gif" type="image/gif" usemap="#map1">
       There are several areas in the library including
       the <A href="reference.html">Reference</A> section and the
       <A href="media.html">Audio Visual Lab</A>.
   </OBJECT>
   <MAP name="map1">
     <AREA shape="rect" coords="0,0,30,30"
           href="reference.html" alt="Reference">
     <AREA shape="rect" coords="34,34,100,100"
           href="media.html" alt="Audio visual lab">
   </MAP>

End example.

7.4.2 Redundant text links for client-side image maps

Checkpoints in this section:

In addition to providing a text equivalent, provide redundant textual links. If the A element is used instead of AREA, the content developer may describe the active regions and provide redundant links at the same time:

Example.

   <OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
   <MAP name="map1">
     <P>Navigate the site.
     [<A href="guide.html" shape="rect"
        coords="0,0,118,28">Access Guide</A>]
     [<A href="shortcut.html" shape="rect"
        coords="118,0,184,28">Go</A>]
     [<A href="search.html" shape="circle"
        coords="184.200,60">Search</A>]
     [<A href="top10.html" shape="poly"
        coords="276,0,276,28,100,200,50,50,276,0">
          Top Ten</A>]
   </MAP>
   </OBJECT>

End example.

Note that in the previous example, the MAP element is the content of the OBJECT element so that the alternative links will only be displayed if the image map (navbar1.gif) is not.

Note also that links have been separated by brackets ([]). This is to prevent older screen readers from reading several adjacent links as a single link as well as to help sighted users distinguish between links visually.

Content developers should make sure they include printable characters (such as brackets or a vertical bar (|)) surrounded by spaces between adjacent text links. The problem does not occur if images have been used as links; The alt-text will not be read as a single link because of the place-holding images that graphical browsers use when images are not loaded. Refer to the section Grouping and bypassing links for more information.

7.4.3 Client-side versus server-side image maps

Checkpoints in this section:

7.4.4 Server-side image maps

Checkpoints in this section:

When a server-side image map must be used, content developers should provide an alternative list of image map choices. There are three techniques:

Server-side and client-side image maps may be used as submit buttons in Forms. For more information, refer to the section Graphical buttons.

7.5 Color in images

Checkpoints in this section:

7.6 Animated images

Checkpoints in this section:

8 Applets and other programmatic objects

While applets may be included in a document with either the APPLET or OBJECT element, OBJECT is the preferred method.

8.1 Text and non-text equivalents for applets and programmatic objects

Checkpoints in this section:

If OBJECT is used, provide a text equivalent in the content of the element:

Example.

  <OBJECT classid="java:Press.class" width="500" height="500">
        As temperature increases, the molecules in the balloon...
  </OBJECT>

End example.

A more complex example takes advantage of the fact the OBJECT elements may be embedded to provide for alternative representations of information:

Example.

  <OBJECT classid="java:Press.class" width="500" height="500">          
     <OBJECT data="Pressure.mpeg" type="video/mpeg">
        <OBJECT data="Pressure.gif" type="image/gif">
           As temperature increases, the molecules in the balloon...
        </OBJECT>
     </OBJECT>
  </OBJECT>

End example.

If APPLET is used, provide a text equivalent with the "alt" attribute and in the content in the APPLET element. This enables the content to transform gracefully for those user agents that only support one of the two mechanisms ("alt" or content).

Deprecated example.

   <APPLET code="Press.class" width="500" height="500"
           alt="Java applet: how temperature affects pressure">
         As temperature increases, the molecules in the balloon...
   </APPLET>

End example.

8.2 Directly accessible applets

Checkpoints in this section:

If an applet (created with either OBJECT or APPLET) requires user interaction (e.g., the ability to manipulate a physics experiment) that cannot be duplicated in an alternative format, make the applet directly accessible.

If an applet creates motion, developers should provide a mechanism for freezing this motion (for an example, refer to [TRACE]). Also, please refer to the next section for information about making audio and video presentations accessible.

For more information about developing accessible applets, please refer to [JAVAACCESS] and [IBMJAVA]. These companies have been developing an Accessibility API as well as making the Java Swing classes accessible.

Related checkpoints:

9 Audio and video

9.1 Audio information

9.2 Text equivalents for multimedia

Checkpoints in this section:

When necessary, a text equivalent should be provided for visual information to enable understanding of the page. For example, consider a repeating animation that shows cloud cover and precipitation as part of a weather status report. Since the animation is supplementing the rest of the weather report (that is presented in natural language - text), a less verbose description of the animation is necessary. However, if the animation appears in a pedagogical setting where students are learning about cloud formations in relation to land mass, then the animation ought to be described for those who can not view the animation but who also want to learn the lesson.

9.3 Embedding multimedia objects

Other objects, such as those requiring a plug-in, should also use the OBJECT element. However, for backward compatibility with Netscape browsers, use the proprietary EMBED element within the OBJECT element as follows:

Deprecated example.

  <OBJECT classid="clsid:A12BCD3F-GH4I-56JK-xyz"
  codebase="//example.com/content.cab" width=100 height=80> 
  <PARAM name="Movie" value="moviename.swf"> 
      <EMBED src="moviename.swf" width=100 height=80 
      pluginspage="//example.com/shockwave/download/"> 
      </EMBED>

      <NOEMBED> 
          <IMG alt="Still from Movie"
                  src="moviename.gif" width=100 height=80> 
      </NOEMBED> 

  </OBJECT>

End example.

For more information refer to [MACROMEDIA].

10 Frames

For visually enabled users, frames may organize a page into different zones. For non-visual users, relationships between the content in frames (e.g., one frame has a table of contents, another the contents themselves) must be conveyed through other means.

Frames as implemented today (with the FRAMESET, FRAME, and IFRAME elements) are problematic for several reasons:

In the following sections, we discuss how to make frames more accessible. We also provide an alternative to frames that uses HTML 4.01 and CSS and addresses many of the limitations of today's frame implementations.

10.1 Providing a frame title

Checkpoints in this section:

Example.

Use the "title" attribute to name frames.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">
<HTML>
<HEAD>
<TITLE>A simple frameset document</TITLE>
</HEAD>
<FRAMESET cols="10%, 90%"
          title="Our library of electronic documents">  
    <FRAME src="nav.html" title="Navigation bar">  
    <FRAME src="doc.html" title="Documents">
    <NOFRAMES>
       <A href="lib.html" title="Library link">   
             Select to go to the electronic library</A>  
    </NOFRAMES>
</FRAMESET>

End example.

10.2 Describing frame relationships

Checkpoints in this section:

Example.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">
<HTML>
  <HEAD>
    <TITLE>Today's news</TITLE>
  </HEAD>

  <FRAMESET cols="10%,*,10%">

  <FRAMESET rows="20%,*">
    <FRAME src="promo.html" name="promo" title="promotions">
    <FRAME src="sitenavbar.html" name="navbar" 
       title="Sitewide navigation bar" longdesc="frameset-desc.html#navbar">
  </FRAMESET>

  <FRAME src="story.html" name="story" title="Selected story - main content" 
     longdesc="frameset-desc.html#story">

  <FRAMESET rows="*,20%">
    <FRAME src="headlines.html" name="index" title="Index of other 
      national headlines" longdesc="frameset-desc.html#headlines">
    <FRAME src="ad.html" name="adspace" title="Advertising">
  </FRAMESET>

  <NOFRAMES>
    <p><a href="noframes.html">No frames version</a></p>
    <p><a href="frameset-desc.html">Descriptions of frames.</a></p>
  </NOFRAMES>

  </FRAMESET>
</HTML>

frameset-desc.html might say something like:

#Navbar - this frame provides links to the major 
          sections of the site:  World News, National News,
          Local News, Technological News,
          and Entertainment News.

#Story  - this frame displays the currently selected story.

#Index  - this frame provides links to the day's 
          headline stories within this section.  

End example.

Note that if the a frame's contents change, the text equivalent will no longer apply. Also, links to descriptions of a frame should be provided along with other alternative content in the NOFRAMES element of a FRAMESET.

10.3 Writing for browsers that do not support FRAME

Checkpoints in this section:

Example.

In this example, if the user reads "top.html":

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">
<HTML>
<HEAD>
<TITLE>This is top.html</TITLE>
</HEAD>
<FRAMESET cols="50%, 50%" title="Our big document">
    <FRAME src="main.html" title="Where the content is displayed">
    <FRAME src="table_of_contents.html" title="Table of Contents">
    <NOFRAMES>
        <A href="table_of_contents.html">Table of Contents.</A>
     <!-- other navigational links that are available in main.html
          are available here also. -->
    </NOFRAMES>
</FRAMESET>
</HTML>

and the user agent is not displaying frames, the user will have access (via a link) to a non-frames version of the same information.

End example.

10.4 Frame sources

Checkpoints in this section:

Content developers must provide text equivalents of frames so that their contents and the relationships between frames make sense. Note that as the contents of a frame change, so must change any description. This is not possible if an IMG is inserted directly into a frame. Thus, content developers should always make the source ("src") of a frame an HTML file. Images may be inserted into the HTML file and their text alternatives will evolve correctly.

Example.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">
<HTML>
<HEAD>
<TITLE>A correct frameset document</TITLE>
</HEAD>
<FRAMESET cols="100%" title="Evolving frameset">
<FRAME name="goodframe" src="apples.html" title="Apples">
</FRAMESET>
</HTML>
   <!-- In apples.html -->
   <P><IMG src="apples.gif" alt="Apples">

End example.

The following deprecated example should be avoided since it inserts IMG directly in a frame:

Deprecated example.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">
<HTML>
<HEAD>
<TITLE>A bad frameset document</TITLE>
</HEAD>
<FRAMESET cols="100%" title="Static frameset">
   <FRAME name="badframe"
          src="apples.gif" title="Apples">
</FRAMESET>
</HTML>

Note that if, for example, a link causes a new image to be inserted into the frame:

  <P>Visit a beautiful grove of 
  <A target="badframe" href="oranges.gif" title="Oranges">oranges</A>

the initial title of the frame ("Apples") will no longer match the current content of the frame ("Oranges").

End example.

10.5 Using FRAME targets

Checkpoints in this section:

Content developers should avoid specifying a new window as the target of a frame with target="_blank".

10.6 Alternatives to frames

One of the most common uses of frames is to split the user's browser window into two parts: a navigation window and a content window. As an alternative to frames, we encourage you to try the following:

  1. Create one document for the navigation mechanism (call it "nav.html"). A separate document means that the navigation mechanism may be shared by more than one document.
  2. In each document requiring the navigation mechanism, include it at the bottom of the document with the following (or similar) OBJECT markup:

    Example.

    <P>
    <OBJECT data="nav.html">
    Go to the <A href="nav.html">table of contents</A>
    </OBJECT>
    

    Putting the navigation mechanism at the end of the document means that when style sheets are turned off, users have access to the document's important information first.

  3. Use style sheets to position the navigation mechanism where you want on the screen. For example, the following CSS rule floats the navigation bar to the left of the page and makes it take up 25% of the available horizontal space:
       OBJECT { float: left; width: 25% }
    

    The following CSS rule attaches the navigation mechanism to the bottom-left corner of the page of the page and keeps it there even if the user scrolls down the page:

       OBJECT { position: fixed; left: 0; bottom: 0 }
    

Note. Navigation mechanisms or other content may be inserted in a document by means of server-side includes.

10.6.1 Sizing frames with relative units

Checkpoints in this section:

In the previous examples, note that frame sizes are specified in percentage. When a user resizes the window, the frames will adjust accordingly and remain readable.

11 Forms

This section discusses the accessibility of forms and form controls that one can put in a FORM element.

11.1 Keyboard access to forms

Checkpoints in this section:

In the next example, we specify a tabbing order among elements (in order, "field2", "field1", "submit") with "tabindex":

Example.

   <FORM action="submit" method="post">
   <P>
   <INPUT tabindex="2" type="text" name="field1">
   <INPUT tabindex="1" type="text" name="field2">
   <INPUT tabindex="3" type="submit" name="submit">
   </FORM>

End example.

This example assigns "U" as the accesskey (via "accesskey"). Typing "U" gives focus to the label, which in turn gives focus to the input control, so that the user can input text.

Example.

 
   <FORM action="submit" method="post">
   <P>
         <LABEL for="user" accesskey="U">name</LABEL>
         <INPUT type="text" id="user">
   </FORM>

End example.

11.2 Grouping form controls

Checkpoints in this section:

Content developers should group information where natural and appropriate. When form controls can be grouped into logical units, use the FIELDSET element and label those units with the LEGEND element:

Example.

<FORM action="//example.com/adduser" method="post">
   <FIELDSET>
   <LEGEND>Personal information</LEGEND>
   <LABEL for="firstname">First name: </LABEL>
   <INPUT type="text" id="firstname" tabindex="1">
   <LABEL for="lastname">Last name: </LABEL>
   <INPUT type="text" id="lastname" tabindex="2">
   ...more personal information...
   </FIELDSET>
   <FIELDSET>
   <LEGEND>Medical History</LEGEND>
   ...medical history information...
   </FIELDSET>
</FORM>

End example.

11.2.1 Grouping menu options

Content developers should group information where natural and appropriate. For long lists of menu selections (which may be difficult to track), content developers should group SELECT items (defined by OPTION) into a hierarchy using the OPTGROUP element. Specifies a label for the group of options with the label attribute on OPTGROUP.

Example.

<FORM action="//example.com/prog/someprog" method="post">
 <P>
 <SELECT name="ComOS">
     <OPTGROUP label="PortMaster 3">
       <OPTION label="3.7.1" value="pm3_3.7.1">PortMaster 3 with ComOS 3.7.1
       <OPTION label="3.7" value="pm3_3.7">PortMaster 3 with ComOS 3.7
       <OPTION label="3.5" value="pm3_3.5">PortMaster 3 with ComOS 3.5
     </OPTGROUP>
     <OPTGROUP label="PortMaster 2">
       <OPTION label="3.7" value="pm2_3.7">PortMaster 2 with ComOS 3.7
       <OPTION label="3.5" value="pm2_3.5">PortMaster 2 with ComOS 3.5
     </OPTGROUP>
     <OPTGROUP label="IRX">
       <OPTION label="3.7R" value="IRX_3.7R">IRX with ComOS 3.7R
       <OPTION label="3.5R" value="IRX_3.5R">IRX with ComOS 3.5R
     </OPTGROUP>
 </SELECT>
</FORM>

End example.

11.3 Labeling form controls

Checkpoints in this section:

An example of LABEL used with "for" in HTML 4.01 is given in the previous section.

A label is implicitly associated with its form control either through markup or positioning on the page. The following example shows how a label and form control may be implicitly associated with markup.

Example.

   <LABEL for="firstname">First name: 
     <INPUT type="text" id="firstname" tabindex="1">
   </LABEL>

End example.

11.4 Graphical buttons

Checkpoints in this section:

Using images to decorate buttons allows developers to make their forms unique and easier to understand. Using an image for a button (e.g., with the INPUT element or BUTTON) is not inherently inaccessible - assuming a text equivalent is provided for the image.

However, a graphical form submit button created with INPUT, type="image" creates a type of server-side image map. Whenever the button is clicked with a mouse, the x and y coordinates of the mouse click are sent to the server as part of the form submission.

In the Image and Image Maps section, we discuss why server-side images ought to be avoided, and suggest using client-side image maps instead. In HTML 4.01, graphical buttons may now be client-side image maps. To preserve the functionality provided by the server, authors have the following options, as stated in the HTML 4.01 Recommendation ([HTML4], section 17.4.1):

If the server takes different actions depending on the location clicked, users of non-graphical browsers will be disadvantaged.
For this reason, authors should consider alternate approaches:

11.5 Techniques for specific controls

Checkpoints in this section:

Example.

Some legacy assistive technologies require initial text in form controls such as TEXTAREA in order to function properly.

<FORM action="//example.com/prog/text-read" method="post">
     <P>
     <TEXTAREA name=yourname rows="20" cols="80">
     Please enter your name here.
     </TEXTAREA>
     <INPUT type="submit" value="Send"><INPUT type="reset">
     </P>
</FORM>

End example.

Provide a text equivalent for images used as "submit" buttons:

Example.

<FORM action="//example.com/prog/text-read" method="post">
<P>
<INPUT type="image" name=submit src="button.gif" alt="Submit">
</FORM>

End example.

Also refer to the section on keyboard access since this applies to form controls.

11.6 Backward compatibility issues for forms

In some HTML 3.2 browsers,

12 Scripts

This section discusses the accessibility of scripts included in a document via the SCRIPT element.

12.1 Graceful transformation of scripts

Checkpoints in this section:

Content developers must ensure that pages are accessible with scripts turned off or in browsers that don't support scripts.

12.2 Scripts that cause flickering

Checkpoints in this section:

12.3 Scripts that cause movement and blinking

Checkpoints in this section:

12.4 Directly accessible scripts

Checkpoints in this section:

An event handler is a script that is invoked when a certain event occurs (e.g, the mouse moves, a key is pressed, the document is loaded, etc.). In HTML 4.01, event handlers are attached to elements via event handler attributes (the attributes beginning with "on", as in "onkeyup").

Some event handlers, when invoked, produce purely decorative effects such as highlighting an image or changing the color of an element's text. Other event handlers produce much more substantial effects, such as carrying out a calculation, providing important information to the user, or submitting a form. For event handlers that do more than just change the presentation of an element, content developers should do the following:

  1. Use application-level event triggers rather than user interaction-level triggers. In HTML 4.01, application-level event attributes are "onfocus", "onblur" (the opposite of "onfocus"), and "onselect". Note that these attributes are designed to be device-independent, but are implemented as keyboard specific events in current browsers.
  2. Otherwise, if you must use device-dependent attributes, provide redundant input mechanisms (i.e., specify two handlers for the same element):

    Note that there is no keyboard equivalent to double-clicking ("ondblclick") in HTML 4.01.

  3. Do not write event handlers that rely on mouse coordinates since this prevents device-independent input.

12.5 Alternative presentation of scripts

Checkpoints in this section:

One way to accomplish this is with the NOSCRIPT element. The content of this element is rendered when scripts are not enabled.

Example.

<SCRIPT type="text/tcl">
 ...some Tcl script to show a billboard of sports scores...  
</SCRIPT>
<NOSCRIPT>     
   <P>Results from yesterday's games:</P> 
   <DL>
      <DT>Bulls 91,  Sonics 80.
      <DD><A href="bullsonic.html">Bulls vs. Sonics game highlights</A> 
      ...more scores...  
   </DL>
</NOSCRIPT>

End example.

12.6 Page updates and new windows

Checkpoints in this section:

13 Index of HTML elements and attributes

Checkpoints in this section:

Elements

Linear version of HTML 4.01 element index.

This index lists all elements in HTML 4.01. The first column of this table links to the definition of the element in the HTML 4.01 specification ([HTML4]). Elements that are deprecated in HTML 4.01 are followed by an asterisk (*). Elements that are obsolete in HTML 4.01 or don't exist in a W3C specification of HTML (2.0, 3.2, 4.01) do not appear in this table.

The second column indicates other W3C specifications for HTML that included each element. The third column indicates the element's role.

The last column lists the sections in the current document where the element is discussed. An entry of "N/A" means that the element is not discussed in this document.

Element name Defined also in Role Techniques
A 2.0, 3.2 Structure N/A
ABBR   Structure N/A
ACRONYM   Structure N/A
ADDRESS 2.0, 3.2 Metadata N/A
APPLET* 3.2 Replaced N/A
AREA 3.2 Structure N/A
B 2.0, 3.2 Presentation N/A
BASE 2.0, 3.2 Processing N/A
BASEFONT* 3.2 Presentation N/A
BDO   Processing N/A
BIG 3.2 Presentation N/A
BLOCKQUOTE 2.0, 3.2 Structure N/A
BODY 2.0, 3.2 Structure N/A
BR 2.0, 3.2 Presentation N/A
BUTTON   Structure N/A
CAPTION 3.2 Structure N/A
CENTER* 3.2 Presentation N/A
CITE 2.0, 3.2 Structure N/A
CODE 2.0, 3.2 Structure N/A
COL   Structure N/A
COLGROUP   Structure N/A
DD 2.0, 3.2 Structure N/A
DEL   Metadata N/A
DFN 3.2 Structure N/A
DIR* 2.0, 3.2 Structure N/A
DIV 3.2 Structure N/A
DL 2.0, 3.2 Structure N/A
DT 2.0, 3.2 Structure N/A
EM 2.0, 3.2 Structure N/A
FIELDSET   Structure N/A
FONT* 3.2 Presentation N/A
FORM 2.0, 3.2 Structure N/A
FRAME   Replaced N/A
FRAMESET   Presentation N/A
H1 2.0, 3.2 Structure N/A
HEAD 2.0, 3.2 Structure N/A
HR 2.0, 3.2 Presentation N/A
HTML 2.0, 3.2 Structure N/A
I 2.0, 3.2 Presentation N/A
IFRAME   Replaced N/A
IMG 2.0, 3.2 Replaced N/A
INPUT 2.0, 3.2 Structure N/A
INS   Metadata N/A
ISINDEX* 2.0, 3.2 Structure N/A
KBD 2.0, 3.2 Structure N/A
LABEL   Structure N/A
LEGEND   Structure N/A
LI 2.0, 3.2 Structure N/A
LINK 2.0, 3.2 Metadata N/A
MAP 3.2 Structure N/A
MENU* 2.0, 3.2 Structure N/A
META 2.0, 3.2 Metadata N/A
NOFRAMES   Alternative N/A
NOSCRIPT   Alternative N/A
OBJECT   Replaced N/A
OL 2.0, 3.2 Structure N/A
OPTGROUP   Structure N/A
OPTION 2.0, 3.2 Structure N/A
P 2.0, 3.2 Structure N/A
PARAM 3.2 Processing N/A
PRE 2.0, 3.2 Presentation N/A
Q   Structure N/A
S*   Presentation N/A
SAMP 2.0, 3.2 Structure N/A
SCRIPT 3.2 (DTD) Processing N/A
SELECT 2.0, 3.2 Structure N/A
SMALL 3.2 Presentation N/A
SPAN   Structure N/A
STRIKE* 3.2 Presentation N/A
STRONG 2.0, 3.2 Structure N/A
STYLE 3.2 (DTD) Processing N/A
SUB 3.2 Presentation N/A
SUP 3.2 Presentation N/A
TABLE 3.2 Structure N/A
TBODY   Structure N/A
TD 3.2 Structure N/A
TEXTAREA 2.0, 3.2 Structure N/A
TFOOT   Structure N/A
TH 3.2 Structure N/A
THEAD   Structure N/A
TITLE 2.0, 3.2 Metadata N/A
TR 3.2 Structure N/A
TT 2.0, 3.2 Presentation N/A
U* 3.2 Presentation N/A
UL 2.0, 3.2 Structure N/A
VAR 2.0, 3.2 Structure N/A

Attributes

Linear version of HTML 4.01 attribute index.

This index lists some attributes in HTML 4.01 that affect accessibility and what elements they apply to. The first column of this table links to the definition of the attribute in the HTML 4.01 specification ([HTML4]). Attributes and elements that are deprecated in HTML 4.01 ([HTML4]) are followed by an asterisk (*). Attributes and elements that are obsolete in HTML 4.01 or don't exist in a W3C specification of HTML (2.0, 3.2, 4.01) do not appear in this table. Attributes that apply to most elements of HTML 4.01 are indicated as such; please consult the HTML 4.01 specification for the exact list of elements with this attribute.

The second column indicates other W3C specifications for HTML that included each attribute. The third column indicates the elements that take each attribute. The fourth column indicates the attribute's role.

The last column lists the sections in the current document where the attribute is discussed. An entry of "N/A" means that the attribute is not discussed in this document.

Attribute name Applies to elements Role Techniques
abbr TD, TH Alternative N/A
accesskey A, AREA, BUTTON, INPUT, LABEL, LEGEND, TEXTAREA User Interface N/A
alt APPLET, AREA, IMG, INPUT Alternative N/A
axis TD, TH Structure N/A
class Most elements Structure N/A
dir Most elements Processing N/A
for LABEL Structure N/A
headers TD, TH Structure N/A
hreflang A, LINK Metadata N/A
id Most elements Structure N/A
label OPTION Alternative N/A
lang Most elements Metadata N/A
longdesc IMG, FRAME, IFRAME Alternative N/A
scope TD, TH Structure N/A
style Most elements Processing N/A
summary TABLE Alternative N/A
tabindex A, AREA, BUTTON, INPUT, OBJECT, SELECT, TEXTAREA User Interface N/A
title Most elements Metadata N/A
usemap IMG, INPUT, OBJECT Processing N/A

The following is the list of HTML 4.01 attributes not directly related to accessibility. Content developers should use style sheets instead of presentation attributes. For event handler attributes, please refer to the section on device-independent event handlers for more detail.

Other structural attributes:
start*, value*, rowspan, colspan, span
Other presentation attributes:
align*, valign*, clear*, nowrap*, char, charoff, hspace*, vspace*, cellpadding, cellspacing, compact*, face*, size*, background*, bgcolor*, color*, text*, link*, alink*, vlink*, border, noshade*, rules, size (deprecated according to element), marginheight, marginwidth, frame, frameborder, rows, cols
Other processing instruction attributes:
ismap, coords, shape
Other user interface attributes:
target, scrolling, noresize
Other metadata attributes:
type, cite, datetime
Event handler attributes:
onblur, onchange, onclick, ondblclick, onfocus, onkeydown, onkeypress, onkeyup, onload, onload, onmousedown, onmousemove, onmouseout, onmouseover, onmouseup, onreset, onselect, onsubmit, onunload

14 References

For the latest version of any W3C specification please consult the list of W3C Technical Reports at //www.tf5x.com.cn/TR.

[CSS1]
"CSS, level 1 Recommendation", B. Bos, H. Wium Lie, eds., 17 December 1996, revised 11 January 1999. This CSS1 Recommendation is //www.tf5x.com.cn/TR/1999/REC-CSS1-19990111. The latest version of CSS1 is available at //www.tf5x.com.cn/TR/REC-CSS1.
[CSS2]
"CSS, level 2 Recommendation", B. Bos, H. Wium Lie, C. Lilley, and I. Jacobs, eds., 12 May 1998. This CSS2 Recommendation is //www.tf5x.com.cn/TR/1998/REC-CSS2-19980512/. The latest version of CSS2 is available at //www.tf5x.com.cn/TR/REC-CSS2.
[HTML4]
"HTML 4.01 Recommendation", D. Raggett, A. Le Hors, and I. Jacobs, eds., 24 December 1999. This HTML 4.01 Recommendation is //www.tf5x.com.cn/TR/1999/REC-html401-19991224/.
[MATHML]
"Mathematical Markup Language", P. Ion and R. Miner, eds., 7 April 1998, revised 7 July 1999. This MathML 1.0 Recommendation is //www.tf5x.com.cn/TR/1998/REC-MathML-19990707/. The latest version of MathML 1.0 is available at //www.tf5x.com.cn/TR/REC-MathML.
[WCAG10]
"Web Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden, and I. Jacobs, eds., 5 May 1999. This WCAG 1.0 Recommendation is //www.tf5x.com.cn/TR/1999/WAI-WEBCONTENT-19990505/.
[WCAG10-CSS-TECHNIQUES]
"CSS Techniques for Web Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden, and I. Jacobs, eds. The latest version of this document is available at //www.tf5x.com.cn/TR/WCAG10-CSS-TECHS/.
[WCAG10-TECHS]
"Techniques for Web Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden, I. Jacobs, eds. This document explains how to implement the checkpoints defined in "Web Content Accessibility Guidelines 1.0". The latest draft of the techniques is available at //www.tf5x.com.cn/TR/WCAG10-TECHS/.

15 Resources

Note: W3C does not guarantee the stability of any of the following references outside of its control. These references are included for convenience. References to products are not endorsements of those products.

15.1 Other guidelines

[IBMJAVA]
IBM Guidelines for Writing Accessible Applications Using 100% Pure Java are available from IBM Special Needs Systems.
[JAVAACCESS]
Information about Java Accessibility and Usability is available from the Trace R&D Center.
[MACROMEDIA]
Flash OBJECT and EMBED Tag Syntax from Macromedia.
[UWSAG]
, G. Vanderheiden, W. Chisholm, eds. The Unified Web Site Guidelines were compiled by the Trace R & D Center at the University of Wisconsin under funding from the National Institute on Disability and Rehabilitation Research (NIDRR),  U.S. Dept. of Education.

15.2 User agents and other tools

A list of alternative Web browsers (assistive technologies and other user agents designed for accessibility) is maintained at the WAI Web site.

[ASTER]
For information about ASTER, an "Audio System For Technical Readings", consult T. V. Raman's home page.
[HYPERMEDIA]
.

15.3 Accessibility resources

[TRACE]
The Trace Research & Development Center. Consult this site for a variety of information about accessibility, including a scrolling Java applet that may be frozen by the user.
[WAI-ER]
The WAI Evaluation and Repair Working Group

16 Acknowledgments

Web Content Guidelines Working Group Co-Chairs:
Jason White, University of Melbourne
Gregg Vanderheiden, Trace Research and Development
W3C Team contact:
Wendy Chisholm
We wish to thank the following people who have contributed their time and valuable comments to shaping these guidelines:
Harvey Bingham, Kevin Carey, Chetz Colwell, Neal Ewers, Geoff Freed, Al Gilman, Larry Goldberg, Jon Gunderson, Eric Hansen, Phill Jenkins, Leonard Kasday, George Kerscher, Marja-Riitta Koivunen, Josh Krieger, Chuck Letourneau, Scott Luebking, William Loughborough, Murray Maloney, Charles McCathieNevile, MegaZone (Livingston Enterprises), Masafumi Nakane, Mark Novak, Charles Oppermann, Mike Paciello, David Pawson, Michael Pieper, Greg Rosmaita, Liam Quinn, Dave Raggett, T.V. Raman, Robert Savellis, Jutta Treviranus, Steve Tyler, and Jaap van Lelieveld

Level Triple-A conformance icon, W3C-WAI Web Content Accessibility Guidelines 1.0

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