anchor.diff:  
   // GRAMMAR OF A TOP-LEVEL DECLARATION
   
  -top_level_declaration : statements? ;
  +// top_level_declaration : statements? ; entrance moved to top.
   
   // GRAMMAR OF A CODE BLOCK
   
  
positive.code:  | extension_declaration
   | subscript_declaration
   | operator_declaration
   ;
  
  declarations : declaration+ ;
  
negative.code:  | Decimal_digit+ '.' Decimal_digit+
   | Decimal_digit+ '.' Decimal_digit+ '.' Decimal_digit+
   ;
  
  // Generic Parameters and Arguments
  
  