This unclear definition make that issue that one XML
document could be valid for one XML processor, but not for others.
It should be fixed that at least from specification
definition that any UNICODE character is valid.
If you think that this is followed this is not true
especially for control characters “#x0000 – #x001F” that is handled
It is possible to rewrite that by “&#” for some
processors, but this not accepted by others. What it is worst I think that this
applied to CDATA sections. So one processor allow “&#”, but not allow that
in CDATA section.
if you think that this character is not often used, that may be wrong e.g.
vertical tab seems to be in use in Microsoft Office.
I hope that you read and not put to bin. I hope that you
also mark that XML version that is obsolete as obsolete.