Closes #3979. As discussed there, this allows for labeled, but
unordered, lists.

Normative changes for implementations:

1. type="" now should work on ul and affect the rendering. The (non-conforming) none/disc/circle/square values still affect the rendering as before.
2. start="" now should work on ul, in the same way it does on ol.
3. The start IDL attribute should be introduced, reflecting the start="" content attribute
4. Determining the ordinal value of <li>s inside <ul>s uses the same algorithm as inside <ol>s, except that reversed="" is ignored.

Things that did not change:

• The values none/circle/square/disc when applied to <ul type=""> still affect the rendering, even if they are non-conforming for authors to use.
• The type IDL attribute still does simple string reflection of the type="" content attribute. (It moved from the obsolete-features section to the main part of the spec, but its behavior is the same.)

Firefox matches (1), (2), and (4). Nobody does (3).

This design was chosen to be as close as possible to Firefox while also being reasonable (thus introducing (3)). Alternate possible designs to discuss:

• Don't bother with start="" at all, so that it has no effect on <ul>.
• Also introduce reversed="" to <ul>, so that the model is exactly the same for both <ol> and <ul>.

Let's discuss in #3979 (not in this PR).

/grouping-content.html ( diff )
/indices.html ( diff )
/obsolete.html ( diff )
/rendering.html ( diff )