Content model nesting failures should not be 4.1.1 failures

[mitchellevan]

Currently

The Nu Validator reports nesting errors like this:

Element X not allowed as child of element Y in this context

Such nesting errors are usually content model errors, not syntax errors. (See discussion: w3c/wcag#978)

The bookmarklet is currently not filtering out content model failures, which should pass WCAG SC 2.1.1 Parsing.

Proposed

In the short term, please add a note in the bookmarklet download page.

Note: When the Nu HTML Validator reports "Element X not allowed as child of element Y in this context", not all such errors are failures of 4.1.1 Parsing. See wcag/issues/978

If it later turns out 4.1.1 is not fully and retroactively deprecated in the WCAG 2.2 time frame, then we might ought to go further and change the bookmarklet filter itself.

[mitchellevan]

4.1.1 now has this retroactive Note. So the bookmarklet documentation (at least) needs updating accordingly.

Here's another response to the current state of the bookmarklet: https://github.com/joe-watkins/nuhtmlchecker-hybrid-parsing-bookmarklet/