What is it?
This test checks for compliance with the Section 508 accessibility standard.
Why it matters
Section 508 is an old standard for web accessibility, that is required for many US organization. It is rapidly being superseded by the newer WCAG 2.0 standard.
How to use it
This test displays a list of failing issues on the left-hand side. Clicking on the page count for any of these issues will display pages with that issue on the right-hand side. Clicking on a page on the right-hand side will open that page in the Inspector:
From here you will typically be presented with a series of questions or issues on the left. Each issue includes buttons allowing you to ignore the issue, or to answer a question about it.