anchor.diff:        {'if', _, _} -> if_expr;
         {'receive', _, _, _, _} -> receive_expr;
         {'receive', _, _} -> receive_expr;
  -      {attribute, _, _, _} -> attribute;
  +      {attribute, _, _, _} ->   attribute;
         {bin, _, _} -> binary;
         {bin_element, _, _, _, _} -> binary_field;
         {block, _, _} -> block_expr;
  
positive.code:       underscore -> true;
        variable -> true;
        warning_marker -> true;
        _ -> false
      end.
  
  
negative.code: %% @see copy_attrs/2
  
  subtrees(T) ->
      case is_leaf(T) of
        true -> [];
        false ->
  	    case type(T) of
  	    application ->
  		[[application_operator(T)], application_arguments(T)];
  	    arity_qualifier ->
  