code: def isnil(self):
          
          nilattr = self.getAttribute("nil", ns=Namespace.xsins)
          return nilattr is not None and (nilattr.getValue().lower() == "true")
docs: Get whether the element is I{nil} as defined by having an
          I{xsi:nil="true"} attribute.
  
          @return: True if I{nil}, else False
          @rtype: boolean