code: function() {
      var captures
        , tok;
      if (captures = /^(not|and|or|is a|is defined|isnt|is not|is)(?!-)\b([ \t]*)/.exec(this.str)) {
        var op = captures[1];
        this.skip(captures);
        if (this.isPartOfSelector()) {
          tok = new Token('ident', new nodes.Ident(captures[0]));
        } else {
          op = alias[op] || op;
          tok = new Token(op, op);
        }
        tok.space = captures[2];
        return tok;
      }
    }
docs: 'not'
  | 'and'
  | 'or'
  | 'is'
  | 'is not'
  | 'isnt'
  | 'is a'
  | 'is defined'