What are the advantages of creating web pages with XML instead of HTML?

Question

From time to time, I see web pages whose content is solely written in XML (not HTML or XHTML). These pages usually have some style sheets (either XSLT or CSS) attached to them w

Answer 1

It's easier to generate it programmatically and reuse it for other purposes than displaying as webpage.

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Update:

EDIT: If this is a good thing, why is it not widespread?

Not everyone needs to generate it programmatically or reuse it for other purposes than displaying as webpage. It's then easier to use plain HTML.