In this example, the problem is not that the author of this document didn't put an alt attribute or textual equivalent attached to the photo element, it's that the designer of the language didn't put the attribute or the proper support in the language itself (that is, in the schema or the DTD). This means that there is no reliable way for a user to find how an author tried to explain a particular image in text form.

This document specifies requirements for XML languages to ensure that people can create documents in a given XML language which are as accessible as possible to people with disabilities, who use a variety of different techniques and tools to access the Web.

Guidelines for designers of XML dialects

This section provides a list of four guidelines, which are general principles of accessible design. Guidelines include rationale and checkpoints. Each checkpoint expresses a requirement, includes some informative text about the checkpoint and one or several Techniques, where implementations and examples of the checkpoint are discussed. Note that the checkpoints are not prioritized at that point.

• Guideline 1. Ensure that authors can associate multiple media objects as alternatives

  Web content providers must able to offer alternative versions of their content if they wish to do so (as the Web Content Accessibility Guidelines tell them to do so). Textual alternatives, like a caption for a movie, or a table summary, can be repurposed for many different output devices, whereas audio content for instance is confined to a certain set of devices (those that can play sound).

  1.1 Provide a mechanism to explicitly associate alternatives for content or content fragments.

  Authors using the elements/attributes in your language must have the ability to provide alternatives for any content, be it images, movies, songs, running text, whatever.

  Techniques for 1.1

  T1.1.1 In SVG, the desc element can be used to describe a graphic.

  desc>An example of a computer network based on a hub
  

  T1.1.2 The summary and the caption elements in the XHTML table module can be used to provide a rich textual description of a non-textual media. cf. WCAG 1.0 checkpoint 1.1.

  summary="This table gives some statistics about fruit
                  flies: average height and weight, and percentage
                  with red eyes (for both males and females)." />
    <caption>Statistics about fruit flies
    
  average
        
  red
  eyes
    
  height
  weight
    
  males
  1.9
  0.003
  40%
    
  females
  1.7
  0.002
  43%
  

  1.2 Define flexible associations, where a given kind of relationship can link to or from objects of varying types without constraint.

  Relationships between alternatives should be explicit in markup to allow users to select which alternatives are useful to them, and should allow multiple types of alternative, not just text as an alternative for an image. For example, the HTML img element lets you provide a text alternative in the alt attribute, but it does not let you explicitly associate images to text or markup. To do this people have to put up with less adequate mechanisms, perhaps by adding "see figure 1" at the end of a paragraph. If the img element could have content, like the object element, this would have solved the problem to some extent. Another way would have been to add an "appliesTo" attribute to the img element, allowing you to put the associated image elsewhere in the document. Satisfying this checkpoint takes a lot of thought due to its subjective nature, but it is very important.

  Techniques for 1.2

  T1.2.1 In technique 1.1.1 we showed that the desc element in SVG can be used to provide an alternative for a graphic. Using a different XML dialect it is possible to add any type of information as part of the desc.

  desc xmlns:mydoc="http://example.org/mydoc">
            The sales bar chart by region
            This description uses markup from the
            mydoc namespace.
         desc>
     
  

  T1.2.2 In the example below, an imaginary mediaExample element allows for any kind of content. In the example, those that have been included are an image, a textual object and a video.

• Guideline 2. Create semantically-rich languages

  Increased structure in an XML application (i.e., elements and attributes that correspond to meaningful terms in the chosen domain) allows authors to encode their knowledge in a manner that user agents can recognize reliably. XML applications deployed on the Web should include linking semantics.

  2.1 Ensure all semantics are captured in markup in a repurposable form.

  XML languages must be designed so that they can be presented in a device independent way. They must be repurposable with respect to input and output devices, as well as spatially independent (don't make the user have to use a mouse), temporally independent (don't require input within a finite time interval), etc.

  Techniques for 2.1

  See SMIL for instance.

  2.2 Separate presentation properties using stylesheet technology/styling mechanisms.

  In non Final-form dialect, authors must be able to mark up documents with proper structural elements and control presentation with style sheets rather than with presentation elements and attributes. This separation of content from presentation facilitates the adaptation to users with different presentational needs (larger font, better contrast, etc) and it also facilitates the maintenance of the pages.

  Techniques for 2.2

  T2.2.2 Example: Right

  Support the inclusion and processing of external style sheets (note the importance of Guideline 4 on exporting semantics in this example, so that the user may override the style)

  mystyle.css: news { text-align: center; font: bold Arial }

  mystyle.css" type="text/css"?> ...
  Story 1
  Story 2

  TW2.2.1 Example: Wrong

  Do not include presentational attributes and elements in your language.

   Story 1
   Story 2

  2.3 Use the standard XML linking and pointing mechanisms (XLink and XPointer). [[Note this checkpoint is under discussion and may change]]

  Xlink [XLINK] and XPointer [XPTR] have been reviewed for accessibility and their linking/pointing semantics may be recognized with certainty.

  Techniques for 2.3

  T2.3.2 Example: Right

  Using links that can be recognized reliably by XLink applications.

  xmlns:xlink="http://www.w3.org/1999/xlink"
           xlink:href="http://mysite/myfile.xml">
        Current List of references
  

  TW2.3.1 Example. Wrong

  User Agents have no way of knowing this is a link.

  
        Current List of references 
  

  2.4 Define element types that allow classification and grouping (header, section, list, etc).

  Make use of existing mechanisms (noting checkpoint 1.2), or create them where necessary, following these guidelines.

  Techniques for 2.4

  T2.4.1 Think in terms of overall structure of your documents when you design a new dialect.

   <-- menu - highest level block element
       appetizer - first child of section, major block element
       entree - second child of section, major block element
       entity meal-sequence - common paragraph level blocks -->
   
   

  2.5 Provide for a full containment model with chunks of reasonable size.

  If a document instance is fully contained, i.e. adequate wrapper elements around PCDATA, then both CSS and XSLT can be used to style content for presentation in alternate formats. If content is in reasonable sized containers, it enables the document to be skimmed quickly by non- visual readers. If a logical hierarchy of elements is used, then a table of contents or summary may be generated providing logical access to document content.

  Techniques for 2.5

  T2.5.1 In this XML Schema example, a document is broken up into a number of sections, and a sequence of nest-able sections with a consistent structure may be used for both navigation and the automated generation of a table of contents to whatever level.

  
   	
  	  	
  	  		
  	  			
  	  			
  	  		
  	  	
  	 
  	 
  	  
  	 	 Section title
  	  
  	 
  	 
  	  	
  	  		
  	  			
  	  			
  	  			
  	  		
  	  	
    
  	 
  

  2.6 Define element types that identify important text content.

  Within most documents, certain elements are key to its understanding. If these are both clear, and identified for machine access, their content can be presented to a user to gain a swift understanding of the semantics of the element, section and eventually the whole document. Examples of such important elements are numbers, dates, titles and links.

  Techniques for 2.6

  T2.6.1 Mark up your text with more semantics, such as datatype meaning "this is a date", or "this is an acronym".
  Code example: Using the XML Schema language [XSCHEMA] to identify data types, rather than simply leaving them as strings: a fully constrained ISBN number:

  2.7 Provide a mechanism for identifying summary / abstract / title.

  Knowing how to extract that information allow User Agents to present it to the end-user, thus facilitating browsing of the content (e.g. deciding if yes or no the document is of interest).

  Techniques for 2.7

  T2.7.1 Example: XML using RDF and Dublin Core elements [DC-elements].

    
     xmlns:dc="http://purl.org/dc/elements/1.1/">
      
        <dc:Title>
            D-Lib Program - Research in Digital Libraries
        
        <dc:Description>The D-Lib program supports the community of 
         people with research interests in digital libraries and 
         electronic publishing.
        
            Corporation For National Research Initiatives
        
        1995-01-07
        World Wide Web Home Page
        text/html
        en
      
    
  
  

  2.8 Don't overload element and attribute names.

  If an element name may be confused, within the context of the document instance, then it is said to be overloaded. If each element name is unique within context it is easier to access the document semantics. Note the relation to checkpoint 4.9.

  Techniques for 2.8

  T2.8.2 Example: Right

   
     
      <price>25price>
      Dollar
  	....
     
    
     Widgets
     <quantity>25quantity>
    
   

  TW2.8.1 Example: Wrong

   
     
      <amount>25 dollarsamount>
      ....
      
    
     Widgets
     <amount>25amount>
    
   

  In the example above, the designer of the schema intended the first occurrence of the element "amount" to mean 'price' of the products purchased and the second occurrence to mean 'quantity' of the products purchased.

  In the example above, the meaning of all the elements is clear and none of the individuals elements is overloaded.

  2.9 Reuse existing accessible modules, as originally specified / intended. [[Note: This checkpoint is under discussion, and may be changed to techniques, or may be augmented with a list of modules that should be re-used]]

  Reusing accessibility modules has the advantage that materials produced using your language will be accessible to their clients. No need to create "new" elements/attributes or re-invent the wheel just to satisfy some creative fantasy. There's a non negligible cost for authors (the people using your language) to learn new concepts. When using modules from other schema, use them with the same semantics as originally intended.

  Techniques for 2.9

  T1.3.1 This example shows how to use an existing DTD module: the object from the XHTML language

  
      xhtml-object-1.mod" >
      %qnames;
      %object;
      ]>
   
   
      etc.
    <xhtml:object...>  
      to include a picture or movie of the part.

  T2.9.1 Example: reusing SMIL switch

    ...
    
      

  2.10 Allow association of metadata with distinct elements and groups of elements.

  This permits authors to make even more semantic associations than what was originally intended by the language designer.

  Techniques for 2.10

  T2.10.1 In SVG for instance, there is a metadata element where RDF statements can be declared, pointing at graphical elements and adding more relational semantics (one object linked to another, or on top of another) than what is provided by SVG itself. See the SVG Accessibility note [SVG-access] for examples.

  Also, by providing ID for all your elements, you allow external metadata to point to them.

  2.11 Specific checkpoint for Final-form applications.

  Languages used only for presentation to a certain scope of users and media are called, Final-form and they should adhere to the following provisions:

  • Allow the author to identify by URI the source used to generate the final form instance.
  • In the application documentation, indicate that final form instances SHOULD NOT be served except upon explicit user request (e.g., through a configured preference).
  • In the application documentation, indicate that final form instances SHOULD NOT be the only form used to store information persistently; a semantically rich source should be stored instead or made available by dereferencing the URI required by the first provision of this checkpoint.

  Techniques for 2.11

  The XSL 1.0 specification [XSL10] contains the following example of such wording.

  In some implementations of XSL/XSLT, the result of tree construction can be output as an XML document. This would allow an XML document which contains formatting objects and formatting properties to be output. This capability is neither necessary for an XSL processor nor is it encouraged. There are, however, cases where this is important, such as a server preparing input for a known client; for example, the way that a WAP (http://www.wapforum.org/faqs/index.htm) server prepares specialized input for a WAP capable hand held device. To preserve accessibility, designers of Web systems should not develop architectures that require (or use) the transmission of documents containing formatting objects and properties unless either the transmitter knows that the client can accept formatting objects and properties or the transmitted document contains a reference to the source document(s) used in the construction of the document with the formatting objects and properties.

• Guideline 3. Design an accessible user interface.

  Web content is rapidly shifting from static pages to dynamic pages, called Web applications. This is most often done using a scripting language based on event callback. The language designers must ensure that the model they chose allows for user control of presentation. Always ensure that nothing in the presentational aspect of the document attempts to restrict user control of how the document instance is accessed.

  3.1 Provide default style sheets for multiple output modalities.

  The additional effort from the language designer point of view in providing style sheets which can represent an XML document instance in alternate modalities is minimal and will have a multiplier benefit for all the authors using the language and these style sheets. Readers of your documents may prefer audio access, so providing an appropriate stylesheet with your schema which will allow those readers to utilize synthetic speech to produce a clear rendering of the content.

  Techniques for 3.1

  T3.1.1 Example: See the sample style sheet for HTML 4.0 [HTML-style] provided with the CSS2 specification.

  3.2 Define navigable structures that allow discrete, sequential, structured, and search navigation functionalities.

  Navigable structures are the key elements used for navigation around an XML application. Define element types that allow classification and grouping, or re-use existing accessible grouping and classification modules.

  Techniques for 3.2

  T3.2.1 Example: See how the Digital Talking Book [DTB] provides elements for navigable structures.

  3.3 Use CSS or XSLT to describe a basic outline view.
  

  The language designer is the best placed to provide a mapping of the new language constructs to a basic outline format, which will facilitate the deployment of content by making it understandable for all classes of users.

  Techniques for 3.3

  T3.3.1 The following stylesheet provides a transformation to produce an HTML outline or table of contents listing the title of each section, and nesting them to match an original document example.

  
  
  
  
  
  
  
   <-- This provides the link back to the full source document -->
   
  full source of document
   
  Outline view
   
    
         
         
        
  
     
   
   
  
  
  
  
  

  3.4 Use a device-independent interaction and events model / module.

  Any XML application which contains user interaction may exclude readership if presumptions are made about the technology used to access that application. What happens when the application only support mouse interaction, and the user is not mouse bound? The result could be lost sales, it will be a loss of interest and a search for alternatives.

  Techniques for 3.4

  T3.4.1 Using DOM2 event the right way in SVG.

  3.5 Allow for user control of interaction timing - rate of change, external events triggering document changes, etc.

  If an XML application presumes that all readers will take in content in a fixed time period, will read at a certain rate, or access each page in a certain time, then readers and users of that application will be lost.

  Techniques for 3.5

  T3.5.1 Ensure and promote the work the user agent has to do to control - on behalf of the end-user - the rate of change of content presentation, perhaps using element attribute for pause facility or settable rate to allow the user control of all interactions. Fixed time period time-outs are not popular. See the SMIL-Animation specification [SMIL-anim] for examples of such design.

• Guideline 4 Document and export semantics

  Make sure that all people can understand your design and map to and from your elements, and easily make assertions about them. Furthermore, make sure that you provide your own first party assertions about your languages: for example, don't make users guess an element's purpose.

  4.1 Provide explicit human readable definitions for markup semantics.

  Any schema which is designed by a single person in a reasonable period will only be understood by that person designing it. When exposed to document authors, interpretations will vary. If the schema designer wishes document authors to utilize the same semantics then those semantics require documentation. The better the quality of that documentation, the more likely the shared understanding.

  Techniques for 4.3

  T4.3.1 Example: TREX

  
      the lowest level block container.
      
  

  4.2 Ensure that at least one version of the XML application's documentation conforms to at least level Double-A of the Web Content Accessibility Guidelines 1.0 [WCAG10].

  Everybody should be able to read and understand a technical specification, even one that is purely intended for a particular class of users.

  Techniques for 4.1

  T4.1.1 For instance, blind users routinely author Web content that is intended for sighted users, and they can do so because the HTML and the CSS specifications are accessible (well structured, description of pictures, etc).

  4.3 Provide a machine-understandable means/mechanism to get from a document instance to the schema.

  This allows programs to automatically retrieve the documentation of a language.

  Techniques for 4.2

  T4.2.2 Example: Uses the W3C XML Schema language as the schema, referencing it via the xsi:schemaLocation attribute.

  
  schemaLocation="http://www.example.org/schemas/doc.xsd"
     	xmlns:my="http://www.jenitennison.com/"
      xmlns="http://www.w3.org/1999/xhtml">

  4.4 Use a schema language that can support explicit human-readable documentation or annotation of semantics.

  It is important that the schema language allows the language designer to explicitly attach documentation to elements and attributes.

  Techniques for 4.4

  T4.4.1 Example Right: The need for the head element is clearly described.

  
   
  	documentation xml:lang="en-US">Title of the section.
      	Required for table of contents generation.
  	
   
  

  T4.4.2 Example Wrong: In the following DTD extract there is documentation available but only by reading the source DTD. It is possible to reliably extract only some of this and present it to a user automatically. It is also not possible to provide rich information here - it is plain text without any of rich media features necessary to provide high-level conformance to WCAG.

  4.5 Provide semantic relationships to other schema where appropriate and possible.

  This allows the authors using the language to reuse their existing knowledge and tools.

  Techniques for 4.5

  T4.5.1 This can be done implicitly via subclassing/derivation of existing types, by asserting equivalence of type (e.g. SVG title and SMIL title) or by mapping to well known semantics.

  Example: mapping the Menu example provided in the Introduction to XHTML using XSLT:

     
      
  Appetizer:    etc...
  
  

  4.6 Document all features of the XML application that benefit accessibility.
  

  This is useful in order to foster the development of state of the art assistive technologies to identify all the features of a new language that make it more accessible.

  Techniques for 4.6

  T4.6.1 SVG has provided a good example of this [SVG10-access] being a part of the recommendation. For W3C Working drafts, include and document those specific features which positively aid accessibility.

  4.7 Include accessibility requirements in conformance requirements.

  This promotes the development of accessible content in the community caring about conformance.

  Techniques for 4.7

  T4.7.1 SVG has specific accessibility requirements as a part [SVG10-access] of the overall requirement document. When the requirements are drawn up, specific clauses need to be included which clearly state accessibility requirements

  T4.7.2 A more detailed explanation is given in section 3.3 of the User Agent Accessibility Guidelines [UAAG10]

  4.8 Document techniques for WCAG, ATAG, and UAAG with respect to the XML application.

  The WAI suite of accessibility guidelines [WCAG],[ATAG],[UAAG] contain detailed descriptions as to how to satisfy each individual document's requirements. Therefore, it is important to review your XML application to ensure that you have implemented a relevant technique for each checkpoint in the WAI suite of accessibility guidelines. For example, you could show how a (hypothetical) instance of your application conforms to WCAG, how an authoring tool which implements your application would enable an author to create accessible content; how a user agent capable of supporting your application must conform to UAAG, etc.

  Techniques for 4.8

  T4.8.1 Still using the MenuML language, here are examples of WCAG techniques

  • WCAG checkpoint 1.1: Provide a text equivalent for every non-text element

    MenuML technique: use the content of the photo element to indicate the textual equivalent of the picture.

  • WCAG checkpoint 3.5: Use header elements to convey document structure and use them according to specification.

    MenuML technique: use the appetizer element to introduce a new appetizer, not a para and some bigger font

  4.9 Do not assume that element or attribute names provide any information about element semantics.

  An element named may have a fully contextualized meaning for the schema author, but is unlikely to mean much to someone who does not speak the language of the author. Equally, taken out of context, without semantic explanation, element names often lose their meaning. Simply naming an element is not enough to assure that document authors will utilize that element in semantic conformance with the schema authors intent. It is likely that confusion and misinterpretation will arise if element or attribute names are relied upon to document a schema.

  Techniques for 4.9

  TW4.9.1 For example, using TREX, avoid colloquial element names.

  Example: Wrong

  
      
      paragraph
      
      
    

  Here the element name has been described using the element name only, which adds no semantic value.

  T4.9.2 Example: Right

  
      
      The lowest level block container.
      
      
      
    

  Here the element name has been described in an alternate form to clarify semantics rather than re-enforce the name by repeating it.

  4.10 Document navigable structures. Describe how discrete, sequential, structured, and search navigation mechanisms should work.

  In order to navigate around a significant document, it is helpful to the reader if they know what elements are available for such navigation.

  Techniques for 4.10

  T4.10.1 Random access to any part of a document via a detailed table of contents, numbered headings which may be searched for, a hierarchical view enabling fast access to sought parts, and a search capability aid in this.