TurtleLexer doesn't accept indentifier with an underscore
rdf:_1 is an existing property in Turtle, but is not recognized by the TurtleLexer.
patterns['PrefixedName'] = r'%(PNAME_NS)s([a-z][\w-]*)' % patterns
should probably get an underscore somewhere. Bounced on this issue when using pygmentize through the LaTeX minted package for highlighting some .ttl files.