anchor.diff:     : stringlist
      | string
      | NUMBER
  -   | tag
  +   | TAG
      ;
   
   testlist
  
positive.code:    ;
  
  test
     : identifier arguments
     ;
  
  stringlist
  
negative.code:    : '\\' OCTETNOTQSPECIAL
     ;
  
  comparator
     : ':comparator' string
     ;
  