sgmlop doesn't do much validation; to quote the homepage: "[sgmlop] is 
tolerant, and happily accepts XML-like data that are not well-formed. If 
you need strictness, use another parser."

But given that Python ships with cElementTree these days, and 
cElementTree's XMLParser (based on expat) is faster than both sgmlop and 
pyexpat, maybe it's time to remove sgmlop support from xmlrpclib...