code: function hookIdentifier(stream) {
      // MySQL/MariaDB identifiers
      // ref: http://dev.mysql.com/doc/refman/5.6/en/identifier-qualifiers.html
      var ch;
      while ((ch = stream.next()) != null) {
        if (ch == "`" && !stream.eat("`")) return "variable-2";
      }
      return null;
    }
docs: `identifier`