Combining XML Documents

Trying to cobble together a set of multiple XML docs that together make up separate sections of a chapter into a single <chapter/> element is raising several interesting issues - e.g. how to cope with explicitly coded section numbers (which really should be generated automatically...Trying to do all the processing in xslt, rather than PHP say, means what I really need is regular expressions - and it seems that xslt 2.0 can offer this: XML.com: Regular Expression Matching in XSLT 2