[xml] Unregistering Input/Output Callbacks?

[Christian Glahn <christian glahn uibk ac at>]

Hello Daniel,

We ran into problems with having "different" parsers using parsers within the 
same process. I already did a lot of workarounds, but uncertainly I ran 
into a problem I realize a missing feature in libxml (or maybe I just have 
overseen something):
While getting through xmlIO I cannot find any function to unregister input or
output callbacks. 

For our case it is important to be able to delete the non-default callbacks 
from the callbackstack. This is required while using XML::LibXML with 
mod_perl on apache. Since modperl keeps the library in memory, the callbacks 
are still resident in memory after the script terminated. 

This leads to situations where a callback of ANOTHER script/ module using
libxml is called by the parser. in some cases this causes script errors 
on the server, because the perlsymbol tables do not match the correct script.
To avoid such problems, it would be great to be able either to remove 
already registered callbacks from the callbackstack (like a pop function)
or reinitialize the callbackstack entirely. 

I wonder if I have overseen such functions (since 
xmlRegisterDefaultInputCallbacks does not reinitialize once it was called).

Thanks in advance
Christian Glahn