[wcag2] "complete start and end tags"

The parsing section states [1]:

> In content implemented using markup languages, elements have
> complete start and end tags

HTML specifies tags that are optional (see e.g. tags that are optional
in HTML 4 [2]). Does guideline 4.1.1 (the guideline and all related
documents seem to be unclear about this) thus disallow what is allowed
in HTML? If yes, why (exactly)? If it does not, is there a chance that
a clarifying note is added, probably to the Errata?


[1] http://www.w3.org/TR/WCAG20/#ensure-compat
[2] http://meiert.com/en/blog/20080601/optional-tags-in-html-4/

-- 
Jens Meiert
http://meiert.com/en/