anchor.diff:  
   fragment
   ESC : '\'\'' ;
  +
  
positive.code: ifStat
      : 'if' expr endStat statBlock 
        ('elseif' expr endStat statBlock)* 
        ('else' endStat statBlock)?
        'end'
      ;
  
  
negative.code:     | ifStat
      | whileStat
      | caseStat
      | expr 
      | NL
      ;
  
  