Fix (sanctioned by Sjoerd) for a problem reported by Andreas Faerber:

gvanrossum · gvanrossum · commit 1f2e09bc45fa · 1999-06-08T21:23:26.000Z
all processing instruction target names containing 'xml' were
rejected, instead (as the standard rejects) only the name 'xml' itself
(or case variants thereof).
diff --git a/Lib/xmllib.py b/Lib/xmllib.py
@@ -495,7 +495,7 @@ def parse_proc(self, i):
                 self.syntax_error('xml:namespace prefix not unique')
             self.__namespaces[prefix] = attrdict['ns']
         else:
-            if string.find(string.lower(name), 'xml') >= 0:
+            if string.lower(name) == 'xml':
                 self.syntax_error('illegal processing instruction target name')
             self.handle_proc(name, rawdata[k:j])
         return end.end(0)
