Gregor Hagedorn writes:

[...] Probably a stylesheet could determine whether only the free text with hidden markup is visible, only the data, or both?

Any ideas, perhaps any technical suggestions, how to achieve that?

XSLT, now an official W3 Recommendation, is the language for transforming XML documents into other XML documents. From the point of view of XSLT, document nodes include text, XML elements, element attributes, comments, and a few other things. This makes it particularly easy to hide or reveal either the text or the markup, or the attributes in various combinations.

Bob Morris