anchor.diff:  
   id
   	: prop_name
  -	| prop_name.id
  +	| prop_name '.' id
   	;
   
   // ---------------------------------------------
  
positive.code: 	;
  
  prop_name_body
  	: _
  	| prop_name_head
  	;
  
  
negative.code: 	;
  
  if
  	: '~if' id ':' statements ':~'
  	| '~if' id ':' statements ':else:' statements ':~'
  	;
  
  
  for
  	: '~for' prop_name 'in' id ':' statements ':~'
  	| '~for' prop_name 'in' id ':' statements ':else:' statements ':~'
  	;
  
  text
  