[xml] How to add a DTD to a document

[Nick Wellnhofer <wellnhofer aevum de>]

I can’t find out how to add a DTD (internal subset) to a document without poking into libxml2’s internal data 
structures. The obvious approach is to add a xmlDtdPtr using 
xmlAddPrevSibling on the document root. But this will cause a memory leak because xmlFreeDoc won’t free the 
DTD nodes. It only frees the DTDs pointed to by doc->intSubset and doc->extSubset. So do I have to deal with 
these struct members manually or is there a better way?

Nick