Suggestion for XHTML2 lists

There are "ordered lists" where the list order matters. Not only the
order, but the exact string used to indentify the item. Think about
software licenses, legal texts, etc. HTML 4 deprecated the start
attribute, implying that numbering is a style thing. This is not always
true, and it would be useful to have titled lists. Why not adding a
label attribute to <ul> this way...

<p>You may do these thing with this software:
</p>
<ul>
<li label="a">Modify it
<li label="b">Distribute it.
</ul>

... it could be added to <ol> but then I don't know what to do with
unlabeled items.