Any disadvantages?

Nothing is ever perfect, and the menu has some disadvantages of its own:

UDM 4 does not provide rich-content or dynamic functionality to Netscape 4 or Internet Explorer 4
They can still see the plain links, but they won't have styling or dynamic behaviors.
Some browsers are only partially-supported
Opera 5 and 6, and Konqueror 3.1 or earlier, can only see the main navigation bar, because they don't support enough scripting to have stable dynamic menus. This is also the case for Mac/IE5 in OS9 or earlier when using a horizontal navbar, and Mozilla browsers 1.2 or earlier when using a relatively-positioned navbar (later versions of these browsers have full support).
It cannot be used inside a WYSIWYG editor
If you open your menu in the "Design View" mode of an editor such as Dreamweaver or FrontPage, it probably won't work; the editor may even re-write its code destructively.
An HTML structure may create more maintenance work for you
Compared with having all the menu data in a single javascript file. This won't be a problem if you use any kind of server-side includes; but if not, it will increase the amount of hand-editing you have to do.

You can mitigate the final issue by having menus that are dynamically generated from data in your configuration file. This approach will reduce the amount of HTML you have to copy-and-paste between pages - only the top list, instead of the whole structure.

UDM 4 could be generated in pure javascript like other menus, but then it wouldn't be properly accessible - you'd still have to provide redundent links in plain HTML, so you may as well make your navigation bar from that in the first place.


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UDM 4 is valid XHTML, and in our judgement, meets the criteria for WAI Triple-A conformance.