anchor.diff:  
   prologue_keyword
       :   'Prologue:';
  - 
  +
   scenario_keyword
   	: 	'Scenario:';
  - 
  +
   step_keyword
   	: 	'Given' | 'When' | 'Then' | 'And' | 'Revering:';
   
  
positive.code:     | '('..')'
      ;
  
  
  WS : [ \t\n\r]+ -> skip ;
negative.code: grammar Gherkins;
  
  
  story
      : feature? prologue? scenario*;
  
  feature
      : feature_keyword title
      ;
  
  
  prologue
      : NEWLINE? prologue_keyword (NEWLINE step)+;
  