code: def getTreesFor(self, document, content_type):
          
  
          # Relative path without potential leading path separator
          # otherwise os.path.join doesn't work
          for rel_path in self.overrides[content_type]:
              if rel_path[0] in ('/', '\\'):
                  rel_path = rel_path[1:]
              file_path = os.path.join(document._cache_dir, rel_path)
              yield etree.parse(utils.xmlFile(file_path, 'rb'))
          return
docs: Provides all XML documents for that content type
          @param document: a Document or subclass object
          @param content_type: a MIME content type
          @return: list of etree._ElementTree of that content type