[XML-SIG] Are question marks allowed in href?

[Krzysztof Nowak]

I'm developing simple xml code. I know that my question is not really
releted to python (at least I'm using pythons twisted.web to write it),
but please, give me simple answer. I have noticed that xml parser is angry
when he is founds this kind of line:

<a
href="http://lipka.desy.de/S1.xhtml?format=png&amp;resolution=320&amp;56=18670&amp;56=18651&56=18652">
SomeLink</a>

I'm think its becouse of question marks. I have menaged to escape the
ampersand but found not answer how to smuggle question mark. Could anybody
help me? I'm shure there's a way to make something like this...

Cheers,
Krzysztof Nowak