anchor.diff:                     s_rdi=name
                      { $s = new LiteralGroupExpression($s_rdi.s); }
                    ;
  -
  -/*
  - * String logic.
  - *
  - * Strings are enclosed in double quotes and may contain escape sequences.
  - * Strings are sensitive to white space.
  - */
  -
  -quoted_identifier returns [ String s = "" ]
  -                 : s1=SQSTRING
  -                   { $s = $s1.getText(); }
  -                 ;
  -regex            returns [ String s = "" ]
  -                 : s1=REGEX
  -                   { $s = $s1.getText(); }
  -                 ;
  -
   
   /*
    * Arithmatic expressions.
  
positive.code:                        )
                         ( qs=QSTRING
                           { expr = regex_transform.apply(expr, $qs.text); }
                         | re=regex
                           { expr = regex_transform.apply(expr, $re.s); }
                         )
                       )
                     )?
  
negative.code:                  @after{ throw new UnsupportedOperationException(); }
                   : identifier
                     ( (EQ_KW|NEQ_KW) constant
                     | (REGEX_MATCH_KW|REGEX_NEGATE_KW) (constant | REGEX)
                     )?
                   ;
  
  