public static function getTypes()
    {
        return array(   self::TT_WORD,
                        self::TT_PHRASE,
                        self::TT_FIELD,
                        self::TT_FIELD_INDICATOR,
                        self::TT_REQUIRED,
                        self::TT_PROHIBITED,
                        self::TT_FUZZY_PROX_MARK,
                        self::TT_BOOSTING_MARK,
                        self::TT_RANGE_INCL_START,
                        self::TT_RANGE_INCL_END,
                        self::TT_RANGE_EXCL_START,
                        self::TT_RANGE_EXCL_END,
                        self::TT_SUBQUERY_START,
                        self::TT_SUBQUERY_END,
                        self::TT_AND_LEXEME,
                        self::TT_OR_LEXEME,
                        self::TT_NOT_LEXEME,
                        self::TT_TO_LEXEME,
                        self::TT_NUMBER
                     );
    }