Message 188329 - Python tracker

It would really help to document that the C API can only use the default xml.etree.ElementTree.TreeBuilder for targets with iterparse (and by extension, IncrementalParser).

I got a nice surprise about that when I went from 3.2 to 3.3 and started getting "TypeError: event handling only supported for ElementTree.TreeBuilder targets".

I included a patch to add notes to iterparse and IncrementalParser, but I'm not sure what to refer to the C module as since xml.etree.cElementTree is deprecated.