Re: BUG #16277: xmlelement allows invalid XML characters when XML version is set to 1.0

Andreas Lennartsson <andreas(at)apkudo(dot)com> writes:
>> On what grounds do you call it invalid?

> Based on the valid control characters for XML 1.0
> https://en.wikipedia.org/wiki/Valid_characters_in_XML

Hm. According to that, C0 control characters *are* legal in XML 1.1,
which would mean that to do this strictly correctly we'd have to
understand the differences between different XML versions, which we
don't --- and, as best I can tell in some quick testing, libxml2
doesn't either. At least, it will happily take random values for the
document version.

xmlroot() just wraps the given XML text in a new outer <xml> declaration,
without any regard for whether the new version number allows or disallows
things that the possibly-implicit version would've allowed before. That
seems of a piece with the generally cavalier treatment of the version
in the rest of xml.c, though.

TBH, it's unlikely that anyone is going to care about this enough
to fix it, even if you could get consensus that making the code
more strict was a good idea. (Backwards compatibility would argue
against that, so I'm not sure such consensus would be easy to get.)
But if you're sufficiently excited about it, you could try submitting
a patch and see what happens.

regards, tom lane