The WAI guidelines

A slightly less verbose version of the guidelines. The original can be found on the W3C web site

Note that all priority 1 checkpoints are needed to meet the NGfL technical annex. Along with keyboard navigation (no mouse) and a frameset must reference valid HTML pages.

Priority 1 checkpoints

 Yes No N/A
In general 1.1 Provide a text equivalent for every non-text element (e.g., via "alt", "longdesc", or in element content). This includes: images, graphical representations of text (including symbols), image map regions, animations (e.g., animated GIFs), applets and programmatic objects, ASCII art, frames, scripts, images used as list bullets, spacers, graphical buttons, sounds, stand-alone audio files, audio tracks of video, and video.      
2.1 Ensure that all information conveyed with colour is also available without colour.      
4.1 Clearly identify changes in the natural language of a document's text and any text equivalents (e.g., captions).      
6.1 Organize documents so they may be read without style sheets.      
6.2 Ensure that equivalents for dynamic content are updated when the dynamic content changes.      
7.1 Avoid screen flickering.      
14.1 Use the clearest and simplest language appropriate for a site's content.      
Images and image maps 1.2 Provide redundant text links for each active region of a server-side image map.      
9.1 Provide client-side image maps instead of server-side image maps except where the regions cannot be defined with an available geometric shape.      
Tables 5.1 For data tables, identify row and column headers.      
5.2 For data tables that have two or more logical levels of row or column headers, use markup to associate data cells and header cells.      
Frames 12.1 Title each frame.      
Applets & scripts 6.3 Ensure that pages are usable when scripts, applets, or other programmatic objects are turned off or not supported.      
Multimedia 1.3 Until user agents can automatically read aloud the text equivalent of a visual track, provide an auditory description of the important information of the visual track of a multimedia presentation.      
1.4 For any time-based multimedia presentation (e.g., a movie or animation), synchronize equivalent alternatives (e.g., captions or auditory descriptions of the visual track) with the presentation.      
If all else fails 11.4 If, after best efforts, you cannot create an accessible page, provide a link to an alternative page that uses W3C technologies, is accessible, has equivalent information (or functionality), and is updated as often as the inaccessible (original) page.      

Priority 2 checkpoints

 Yes No N/A
In general 2.2 Ensure that foreground and background colour combinations provide sufficient contrast [Priority 2 for images, Priority 3 for text].      
3.1 When an appropriate markup language exists, use markup rather than images to convey information.      
3.2 Create documents that validate to published formal grammars.      
3.3 Use style sheets to control layout and presentation.      
3.4 Use relative rather than absolute units in markup language attribute values and style sheet property values.      
3.5 Use header elements to convey document structure and use them according to specification.      
3.6 Mark up lists and list items properly.      
3.7 Mark up quotations. Do not use quotation markup for formatting effects such as indentation.      
6.5 Ensure that dynamic content is accessible or provide an alternative presentation or page.      
7.2 Avoid causing content to blink.      
7.4 Do not create periodically auto-refreshing pages.      
7.5 Do not use markup to redirect pages automatically. Instead, configure the server to perform redirects.      
10.1 Do not cause pop-ups or other windows to appear and do not change the current window without informing the user.      
11.1 Use W3C technologies when they are available and appropriate for a task and use the latest versions when supported.      
11.2 Avoid deprecated features of W3C technologies.      
12.3 Divide large blocks of information into more manageable groups where natural and appropriate.      
13.1 Clearly identify the target of each link.      
13.2 Provide metadata to add semantic information to pages and sites.      
13.3 Provide information about the general layout of a site (e.g., a site map or table of contents).      
13.4 Use navigation mechanisms in a consistent manner.      
Tables 5.3 Do not use tables for layout unless the table makes sense when linearised.      
5.4 If a table is used for layout, do not use any structural markup for the purpose of visual formatting.      
Frames 12.2 Describe the purpose of frames and how frames relate to each other if it is not obvious by frame titles alone.      
Forms 10.2 For all form controls with implicitly associated labels, ensure that the label is properly positioned.      
12.4 Associate labels explicitly with their controls.      
Applets & scripts 6.4 For scripts and applets, ensure that event handlers are input device-independent.      
7.3 Avoid movement in pages.      
8.1 Make programmatic elements such as scripts and applets directly accessible or compatible with assistive technologies [Priority 1 if functionality is important and not presented elsewhere, otherwise Priority 2.]      
9.2 Ensure that any element that has its own interface can be operated in a device-independent manner.      
9.3 For scripts, specify logical event handlers rather than device-dependent event handlers.      

Priority 3 checkpoints

 Yes No N/A
In general 4.2 Specify the expansion of each abbreviation or acronym in a document where it first occurs.      
4.3 Identify the primary natural language of a document.      
9.4 Create a logical tab order through links, form controls, and objects.      
9.5 Provide keyboard shortcuts to important links, form controls, and groups of form controls.      
10.5 Include non-link, printable characters (surrounded by spaces) between adjacent links.      
11.3 Provide information so that users may receive documents according to their preferences (e.g., language, content type, etc.)      
13.5 Provide navigation bars to highlight and give access to the navigation mechanism.      
13.6 Group related links, identify the group, and provide a way to bypass the group.      
13.7 If search functions are provided, enable different types of searches for different skill levels and preferences.      
13.8 Place distinguishing information at the beginning of headings, paragraphs, lists, etc.      
13.9 Provide information about document collections (i.e., documents comprising multiple pages.).      
13.10 Provide a means to skip over multi-line ASCII art.      
14.2 Supplement text with graphic or auditory presentations where they will facilitate comprehension of the page.      
14.3 Create a style of presentation that is consistent across pages.      
Images 1.5 Provide redundant text links for each active region of a client-side image map.      
Tables 5.5 Provide summaries for tables.      
5.6 Provide abbreviations for header labels.      
10.3 Provide a linear text alternative (on the current page or some other) for all tables that lay out text in parallel, word-wrapped columns.      
Forms 10.4 Include default, place-holding characters in edit boxes and text areas.