code: private function doDiff($from_text, $to_text)
      {
          $this->last_edit = false;
          $this->stackpointer = 0;
          $this->from_text = $from_text;
          $this->from_offset = 0;
          // can't diff without at least one granularity specifier
          if (empty($this->granularityStack)) {
              return;
          }
          $this->_processGranularity($from_text, $to_text);
      }
docs: Entry point to compute the diff.