[xml] Allow invalid XML characters in tag names

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

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I've been working with an HTML5 that uses libxml2's DOM structure as the
output format, and have been running into some problems when dealing
with some types of tags, for example, <a@>. According to the HTML5 spec,
this should be directly inserted into the DOM as such, but this tag name
is invalid XML and libxml2 chokes on it.

Is there any way to "relax" libxml2's character requirements for these
things?
- --
 Edward Z. Yang                        GnuPG: 0x869C48DA
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