hand-wavy unicode problems

Hi,

I apologize if the terminology I'm using is not correct but hopefully
an example will clarify
what I mean.

Is there any way you can force the output to use character codes
instead of the corresponding
characters.

e.g. I've got this in the input

<elem attr="some val?"/>

and I need the output to be

<elem attr="some val&#63;"/>

instead of

<elem attr="some val?"/>

I think it shouldn't matter but it does seem to matter for the system
I'm generating xml input
for.  Is there a way I can force the output to be like the first example?

Thanks,
Andy