code: def indexableText(self, tree):
          
          rval = set()
          root = tree.getroot()
          for txp in self.text_elts_xpaths:
              elts = txp(root)
              texts = []
              # Texts in element may be empty
              for elt in elts:
                  text = self.text_extract_xpath(elt)
                  if len(text) > 0:
                      texts.append(text[0])
              texts = self.separator.join(texts)
              texts = [toUnicode(x) for x in self.wordssearch_rx.findall(texts)
                       if len(x) > 0]
              rval |= set(texts)
          return rval
docs: Provides the indexable - search engine oriented - raw text
          @param tree: an ElementTree
          @return: set(["foo", "bar", ...])