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Description of Accessibility Requirements for WP
The page clarifies accessibility requirements for WP design. It explains the user requirements at the conceptual level. It does not intend to provide success criteria or techniques like WCAG, however success criteria or techniques may be developed on basis of this page.
Visually it is easy to take in a whole screen or page of information. The eye naturally identifies structures such as sidebars, paragraphs, headings, and lists. The screen reader user and other users using Assistive Technology (AT) must rely on the semantic structures to read quickly and efficiently. A screen reader will use the DOM for presenting information and also aide in navigation. It is easy to move to the next heading or block of text, provided the structures are marked up properly. For example on Windows, pressing the “h” key will take the screen reader user to the next heading. Pressing the down arrow key reads each line, and pressing ctrl+down arrow takes you to the next block item. When there is a sidebar with the word “caution” it is very important that the item is read before the paragraph that is potentially dangerous. To the sighted reader, this is obvious, but to the person using AT, the proper reading order is essential. This is easy to implement, because the sidebar is before the paragraph in the HTML, and the CSS positions the sidebar next to the paragraph. Hence, the ability to navigate by headings and block items and the proper reading order is essential.
WP can consist of multiple resources, so this meaningful reading order and navigation should work across multiple files/resources. If the publication is in form of a decision tree then it is up to the user to select the article or section, but within the article or section itself, the reading order must be preserved.
Based on this explanation, the navigation for WP can be of 2 types:
- Local navigation: This is the navigation within a file or resource. For example proper structure of headings in an HTML file.
- Global navigation: This is navigation across the constituent files or resources of the publication.
Guidance for local navigation is covered quite well by WCAG 2.0, but the global navigation in the context of web publications is not covered so extensively, therefore this document will focus more on global navigation.
The nearest equivalent of navigation requirements for web publication in WCAG 2.0 is navigation requirements for set of web pages. The following 2 sections in WCAG 2.0 provide guidance for navigation:
2.4.5 Multiple Ways: More than one way is available to locate content within a set of Web pages where content is not the result of, or a step in, a process. http://www.w3.org/WAI/WCAG20/quickref/20070517/Overview.php#navigation-mechanisms-mult-loc
2.4.7 Location: Information about the user's location within a set of Web pages is available.
http://www.w3.org/WAI/WCAG20/quickref/20070517/Overview.php#navigation-mechanisms-location
To achieve the above two sections, WP needs to preserve hierarchy of the publication and provide additional navigation as per the requirement of the content and the structure of the publication. This splits the requirements in two categories, explained as follows:
The navigation to sections/headings in right hierarchical order is essential. In WP the hierarchy can span across multiple content resources. So, WP must be able to express the hierarchy of sections spread across multiple content resources.
It mainly includes the navigation specified by the author for the convenience of the readers for example page numbers, additional notes, landmarks etc.
Note: The following principles lay down the user requirements, without going through the details like whether the default reading order will be provided in manifest or will be implemented with next/previous links etc. The requirements also do not get into details of browser VS reading system implementation, and mainly focus on the user' expectations.
Navigation and default reading order are two different items. For accessibility, navigation across multiple resources is more important than default reading order across multiple resources. Based on discussions in PWG, it is important to highlight the following points:
- For the resources in default reading order, continuous reading experience is required. In other words, the user should be able to move from end of a content resource to the next content resource without additional steps of going through TOC, pagelist etc.
- Ideally navigation to all content resources is required, but there can be some flexibility in some situations, explained in the following points.
- If there is default reading order which lists all the content resources then author can be given flexibility to exclude some of these content resources from navigation, provided that excluding the content resource from navigation does not hinder the publication from expressing the hierarchy and direct access to print equivalent pages, important landmarks etc.
- If there are content resources that are not covered by the default reading order (e.g. decision tree based traversal in publication) then navigation must ensure access to these content resources. The publication can also have auxiliary content like extended descriptions, but these requirements do not go so deep at this early stage.
In all the above scenarios, user agent should be able to inform users about their current reading location in WP. At minimum it needs to include the information about the section and print equivalent page number if it exists.