Progressive enhancement
For the purposes of graded browser support, web technologies have been separated into the following layers (equivalent alternative formats have been specified where they are required to ensure all content is accessible):
| Web technologies | Equivalent alternative format required (IS26 / WCAG) |
|---|---|
| HTML/XHTML (including forms and/or ARIA semantics) |
None |
| Media (JPEG, PNG, GIF, SVG, Audio, Video) |
Plain text or HTML/XHTML |
| Downloadable documents (open formats) |
Multiple formats should be provided to ensure users without particular software are not disadvantaged |
| Web technologies | Equivalent alternative format required (IS26 / WCAG) |
|---|---|
| CSS | None (also, do not use deprecated HTML or presentational attributes as an alternative) |
| Background images | None |
| Web technologies | Equivalent alternative format required (IS26 / WCAG) |
|---|---|
| JavaScript (Unobtrusive DHTML) | None (Content Layer must be sufficient) |
| Ajax (Hijax) | None (Content Layer must be sufficient) |
| Flash | HTML/XHTML (Optionally with media) |
Websites and web applications must be functional for all browsers that support the content layer technologies used (even if they don’t support presentation layer or behaviour layer technologies).
Whenever possible a progressive enhancement approach should be used to add layers based on browser capabilities (try to limit use of hacks, workarounds or browser-sniffing).
