link for review

I think

If headings are organized into a logical outline, the aria-level attribute is used to indicate the nesting level.

needs rewording now that aria-level is required.

Something like:

Headings SHOULD be organized into a logical outline, and the aria-level attribute MUST be used to indicate the nesting level.

?

@jnurthen @carmacleod

In the spirit of simplifying shoulds/musts, how about:

To ensure headings are organized into a logical outline, authors MUST use the aria-level attribute to indicate the proper nesting level.

Made the suggested change!

As a quick question about the accessibility tree mappings, what heading level will a heading have if there is no implicit level?
Thanks, Bryan

As a quick question about the accessibility tree mappings, what heading level will a heading have if there is no implicit level?
Thanks, Bryan

http://w3c.github.io/aria/#document-handling_author-errors_states-properties states

If a required WAI-ARIA attribute for a given role is missing, user agents SHOULD process the attribute as if the values given in the following table were provided.
In the table the fallback for aria-level is 2

So not supplying a heading level is now an author error, but if a browser is following the fallback guidance it should still expose it with a level of 2.

Excellent, thanks, that was my only concern with this.