def WhatActorsArePresent(self):
results = []<EOL>for E in self.header_elements:<EOL><INDENT>a = _find_actor(E)<EOL>if a not in [ None, SOAP.ACTOR_NEXT ]: results.append(a)<EOL><DEDENT>return results<EOL>
Return a list of URI's of all the actor attributes found in
        the header.  The special actor "next" is ignored.