Validating DataGroup children

Hi,

I have a popup (TitleWindow) with Form,

which has a DataGroup, consisting of a number of "rows",

which have some GUI widgets (TextInputs, DropDownLists, ComboBoxes, etc)

in ItemRenderer.

I do validate data on that Form.

But how can I do validation of data which user fills on these children rows
(in ItemRenderer)?

TIA,

Oleg.