Pointer to a good explanation of tree-fragments and n

Could someone please point me to a good discussion of tree-fragments
and node-sets? I'm getting to the point of using them in a trial and
error way and I'm not happy with it.

What I'm interested in is to understand the architectural differences
and when and why I can use one or the other in certain contexts. Other
issues are questions like 'what operation will create which one of
them'.

I don't mind bying a book for it, but the books I have so far are not
going into much detail and not providing lots of examples.

Thanks,


--
Ferdinand Soethe