def invalid_marker(text):
try:<EOL><INDENT>evaluate_marker(text)<EOL><DEDENT>except SyntaxError as e:<EOL><INDENT>e.filename = None<EOL>e.lineno = None<EOL>return e<EOL><DEDENT>return False<EOL>
Validate text as a PEP 508 environment marker; return an exception
if invalid or False otherwise.