anchor.diff:   	)
    ;
   
  + /** Number (base ten) */
    NUM
    :
    	[0-9]+
    ;
   
  + /** White Space */
    WS
    :
    	[ \t\r\n]+ -> skip
    ;
   
  + /** String */
    STRING
    :
    	'"'
  
positive.code:  	| '<='
   ;
  
   bool_val
   :
   	'TRUE'
   	| 'FALSE'
   ;
  
   categ_attr
   :
   	ID '.' ID
   ;
  
   str_val
   :
   	categ_attr
   	| STRING
   ;
  
   str_comp
   :
   	'='
   	| '<>'
   ;
  
   ID
   :
   	LETTER
  
negative.code: 
   ;
  
   /** One rule of the policy. action is PERMIT by default. Target and condition are optional*/
   pol_rule
   :
   	'rule' ID 'begin'
   	(
   		'action' action_id
   	)?
   	(
   		'target' condition
   	)?
   	(
   		'condition' condition
   	)? 'end'
   ;
  
   /** This applies to target and condition indistinctly. This is valid if you use YAAL as an 
    * understanding tool, but it does not suffice to generate XACML code
    */
   condition
   :
  