Enhance Example Section in Doc (fragid/set-xml-id)

[tomschr]

We have an Example section in usage.rst. I think, this section deserves some more example.

Especially a short example showing the new fragid and set-xml-id attributes. One solution would be to name the subsections as a kind of "use case scenario". For example, "Including parts of an XML document" or "Changing ID of Root Element". Something like that.

Another idea would be to place the examples in the manpage.

[Vogtinator]

IMO that's already handled in the DocBook transclusion document: http://docbook.org/docs/transclusion/#tutorial

[tomschr]

Ok. Maybe not the full example. But a short list about the possible XInclude attributes and their meaning would be very useful (maybe in the manpage?)