anchor.diff:  
   availability_argument : Platform | '*' ;
   
  -/** Must match as token so Platform_version doesn't look like a float literal */
   Platform : Platform_name WS? Platform_version ;
   
   fragment
  
positive.code: 
  // GRAMMAR OF A TOP-LEVEL DECLARATION
  
  top_level_declaration : statements? ;
  
  // GRAMMAR OF A CODE BLOCK
  
  
negative.code: 
  top_level : statement* EOF ;
  
  // GRAMMAR OF A STATEMENT
  
  statement
  