[xml] Use of xmlValidate* functions in tree

["Edward Z. Yang" <edwardzyang thewritingpot com>]

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When manipulating libxml2's tree, when is it required to call the
xmlValidate*() functions? I did some testing, and it seems that libxml2
will happily create attributes or elements that do not conform to the
lexical space of Name, etc. When the tree is serialized the XML is
invalid, but libxml2 doesn't explode or anything like that.

Also, I'm curious to know where lies the burden for checking the
validity of these things. Is the client code expected to check? If so,
is there a "safe" wrapper that will automatically do the checks? I
understand that it's more efficient not to check if not strictly
necessary, but it's easy to miss a precondition here or there if you're
not paying attention.

I should note that my C knowledge is abysmal to none, so if I'm just
blithering nonsense, please say so. :-)
- --
 Edward Z. Yang                        GnuPG: 0x869C48DA
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