Algorithm for Insertion of tags w/o breaking well-formedness

[sylvain.loiseau]

Probably a classical question, but I didn't find information anywhere. I
have to XML files whose "textual" content (the content of the text nodes)
are identical, but with some differents start and endElement. I would like
to merge the two and I look for an algorithm for deciding where insert each
element from one document into the other, since such a code should probably
exist. I am in a SAX context but could adapt the environment.

Thanks in advance,
SL