code: public function explainFlag($flags, $explanation)
      {
          $flags                = is_array($flags) ? $flags : array($flags);
          $this->flag_sets[]    = $flags;
          $this->explanations[] = $explanation;
      }
docs: Adds the explanation for a group of flags that all
  have the same function.
  
  @param string/array $flags       Flag and alternates. Don't
  worry about leading dashes
  as these are inserted automatically.
  @param string       $explanation What that flag group does.