code: def query(dom, query, context=None, tagid=None):
          
          if context is None:
              source = dom
          else:
              source = context
  
          if tagid is None:
              return source.xpath(query, namespaces=OneLogin_Saml2_Constants.NSMAP)
          else:
              return source.xpath(query, tagid=tagid, namespaces=OneLogin_Saml2_Constants.NSMAP)
docs: Extracts nodes that match the query from the Element
  
          :param dom: The root of the lxml objet
          :type: Element
  
          :param query: Xpath Expresion
          :type: string
  
          :param context: Context Node
          :type: DOMElement
  
          :param tagid: Tag ID
          :type query: String
  
          :returns: The queried nodes
          :rtype: list