anchor.diff:  %%
   %%	is_tree(Wrapper) = false
   
  --record(wrapper, {type, attr = #attr{}, tree}).
  +-record(wrapper, {type           :: atom(),
  +		  attr = #attr{} :: #attr{},
  +		  tree           :: term()}).
  +
  +%% =====================================================================
  +
  +-type syntaxTree() :: #tree{} | #wrapper{} | tuple(). % XXX: refine
   
   %% =====================================================================
   %%
  
positive.code:       Node1 -> (data(Node1))#list_comp.body
      end.
  
  %% =====================================================================
  %% @spec query_expr(Body::syntaxTree()) -> syntaxTree()
  %%
  
negative.code: 			[[attribute_name(T)], As]
  		    end;
  	    binary -> [binary_fields(T)];
  	    binary_comp ->
  		    [[binary_comp_template(T)], binary_comp_body(T)];
  	    binary_field ->
  		case binary_field_types(T) of
  		  [] -> [[binary_field_body(T)]];
  		  Ts -> [[binary_field_body(T)], Ts]
  		end;
  	    binary_generator ->
  		    [[binary_generator_pattern(T)], 
                       [binary_generator_body(T)]];
  	    block_expr -> [block_expr_body(T)];
  	    case_expr ->
  		[[case_expr_argument(T)], case_expr_clauses(T)];
  