Language Differences and Testing Methodology
Testing accessibility was so /easy/ once upon a time! Ok, not really, but it was possible to assume that the markup language used would be one form or other of HTML. Even with so–called technology–agnostic guidelines such as WCAG 2 the rules did not change: checking a document for headers meant checking for the h1 throuhgh h6 elements.
This /was/ simple, and consistent. With the development of languages like XHTML 2 and HTML 5 the rules change — what is and isn’t a header is no longer as easy to determine.
In XHTML 2, for example, the presence of an h–element is sufficient to pass WCAG 2 SC 1.3.1, while at the same time a h–element in HTML 4 or 5 (per March 2009) would fail the same.
In all of this we try not to think too much about extensibility the “Semantic Web” way. That would require thinking about how to actually map element <foo:bar> to something identifiable as a header.
We are thinking of predefined languages, however, which is why changes to siteSifter are drafted to ensure that we can, in the future, test for the right things depending on the markup language used.