procedure TVST_Sort.IncrementalSearch(
  Sender: TBaseVirtualTree; Node: PVirtualNode;
  const SearchText: WideString; var Result: Integer);
var
  a, b: String;
begin
  a:=AnsiLowerCase(SearchText);
  if node<>nil then
    b:=AnsiLowerCase(TVirtualStringTree(sender).Text[node, sender.FocusedColumn])
  else
    b:='';
  result:=StrLIComp(PChar(a), PChar(b), Min(length(a), length(b)));
end;

  with meinvst do
  begin
    IncrementalSearch:=isVisibleOnly;
    IncrementalSearchTimeout:=1000;
    if not Assigned(OnIncrementalSearch) then
      OnIncrementalSearch:=TVST_Sort.IncrementalSearch;
  end;