anchor.diff:    class_decl
     methods
     method
  +  class_method
     functions
     function
     body
  
positive.code: 
  %% Method declarations
  method -> function : '$1'.
  
  %% Valid function names
  function_name -> function_identifier : ?identifier_name('$1').
  
negative.code:     block = '$3'#args.block,
      body  = '$5'
    }.
    
  %% Class declarations
  class_decl -> class module_name methods 'end' : 
  