code: def relaxng(cls, includechildren=True,extraattribs = None, extraelements=None, origclass = None):
          
          E = ElementMaker(namespace="http://relaxng.org/ns/structure/1.0",nsmap={None:'http://relaxng.org/ns/structure/1.0' , 'folia': "http://ilk.uvt.nl/folia", 'xml' : "http://www.w3.org/XML/1998/namespace",'a':"http://relaxng.org/ns/annotation/0.9" })
          if not extraattribs:
              extraattribs = []
          extraattribs.append(E.optional(E.attribute(E.text(), name='set')) )
          return AbstractElement.relaxng(includechildren, extraattribs, extraelements, cls)
docs: Returns a RelaxNG definition for this element (as an XML element (lxml.etree) rather than a string)