UDM 4 is valid XHTML, and in our judgement, meets the criteria for WAI Triple-A conformance.
Doctypes make no functional difference to the menu - the structure is valid HTML and XHTML, and works correctly with any doctype.
However they do make a visual difference, because the menu widths will vary according to rendering mode, which is determined in-part by the page's doctype. (The dimensions of the navigation bar do not vary like this - they're designed to be box-model resistant.) The rendering mode can also make a behavioral difference in Internet Explorer, where a very large menu structure will be noticeably faster on a page in Standards mode, compared with the same page in Quirks mode.
Mime-types only make a difference to one specific configuration - if your page is served as
application/xhtml+xml (or similar) then you cannot use
dynamically-generated menus, because
they're appended using innerHTML, which won't necessarily work in that environment.
But this needn't be a problem,
as there are two extensions available which offer compatible functionality:
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