Description:
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It would be useful to have a unicode error mode that threw exceptions on 
an error: this would make it possible to have different behaviour an 
error. Currently all that is possible is creating a custom error handler 
and acting differently depending on what the error string is: can an 
error string really be relied upon to never change? I doubt it.

What practical use, though? Most obviously, checking if a string is 
valid under a certain encoding. This is needed when processing real-
world XML data, due to the vast amount sent with the wrong encoding.