anchor.diff:                   | item_impl
                    | item_struct
                    ]
  -        { printf("item_or_view_item\n"); }
       ;
   
   /// 6.1.1 Type Parameters
  
positive.code: /// 7.2.9 Index expressions - handled by dot_or_call_expr
  /// 7.2.10 Unary operator expressions
  prefix_expr
      : [ '!' prefix_expr
      | '-' prefix_expr
      | '*' prefix_expr
      | '&' /* LIFETIME? */ MUT? prefix_expr // ambiguity: lifetime after & may be a loop label
      | '~' prefix_expr
      | BOX prefix_expr // ambiguity: what to do with box ( expr? )?
      | dot_or_call_expr
   ] { printf("prefix_expr\n"); }
      ;
  
  /// 7.2.11 binary operator expressions
  
negative.code: rust : crate ;
  
  // 5. Crates and source
  crate : inner_attr* mod_item* ;
  
  // 6. Items and Attributes
  /// 6.1 Items
  