anchor.diff:  
   -spec pretty_from_box([#box{}] | #box{}) -> binary().
   pretty_from_box([]) -> [];
  -pretty_from_box(#box{collapsed=true}=Box) -> flat_from_box(Box);
   pretty_from_box(#box{name= <<>>,children=[]}) -> <<>>;
   pretty_from_box(#box{ind=Ind,name=Name,children=[]}) ->
       iolist_to_binary([indent(Ind), Name, "\r\n"]);
  
positive.code: pretty_from_box(#box{ind=Ind,name= <<>>,children=CH}) ->
      if
          (hd(CH))#box.collapsed ->
              iolist_to_binary([indent(Ind+1),[flat_from_box(C) || C <-CH],"\r\n"]);
          true ->
              iolist_to_binary([[pretty_from_box(C) || C <-CH]])
      end;
  pretty_from_box(#box{ind=Ind,name=Name,children=CH}) ->
      if
          (hd(CH))#box.collapsed ->
              iolist_to_binary([indent(Ind),binary_to_list(Name),"\r\n",
                  indent(Ind+1),[flat_from_box(C) || C <-CH],"\r\n"]);
          true ->
              iolist_to_binary([indent(Ind), Name,"\r\n",[pretty_from_box(C) || C <-CH]])
      end;
  pretty_from_box([Box|Boxes]) ->
  
negative.code: -include("dderl.hrl").
  -include("dderl_sqlbox.hrl").
  
  -define(DefCollInd,6).  % First indentation level which will be collapsed by default
  -define(DefCollLen,40). % Max length of flattened subboxes which is collapsed
  
  -spec validate_children([#box{}]) -> ok | {error, binary()}.
  validate_children([]) -> ok;
  