code: function hookVar(stream) {
      // variables
      // @@prefix.varName @varName
      // varName can be quoted with ` or ' or "
      // ref: http://dev.mysql.com/doc/refman/5.5/en/user-variables.html
      if (stream.eat("@")) {
        stream.match(/^session\./);
        stream.match(/^local\./);
        stream.match(/^global\./);
      }
  
      if (stream.eat("'")) {
        stream.match(/^.*'/);
        return "variable-2";
      } else if (stream.eat('"')) {
        stream.match(/^.*"/);
        return "variable-2";
      } else if (stream.eat("`")) {
        stream.match(/^.*`/);
        return "variable-2";
      } else if (stream.match(/^[0-9a-zA-Z$\.\_]+/)) {
        return "variable-2";
      }
      return null;
    }
docs: variable token