anchor.diff:      ;
   
   pseudo
  -    : Colon Colon? ( identifier | functionalPseudo )
  +    : Colon Colon? ( interpolation | identifier | functionalPseudo )
       ;
   
   functionalPseudo
  
positive.code:     | hexcolor
      | ifExpression
      | functionCall
      | plusMinus? Lparen ws expression Rparen ws
      ;
  
  ifExpression
  
negative.code:     ;
  
  identifier
      : ( VendorPrefix  | Minus )? Ident
      | From
      | To
      ;
  