Accessibility: Add accessibility guidelines #866
Description
We don't currently have any guidelines for accessibly development, which may result in inconsistencies.
We should document accessibility best practices as they apply to development of Silverstripe CMS.
Some things to include are:
- What web accessibility standards we strive to achieve
- Information about "tab islands" and when to use them
- Other keyboard navigation/operation information (e.g. how to deal with drag/drop)
- A link to the W3C patterns as a guide
There are probably other things we should note, as well.