[2008] Clear contents of textbox, reverting transaction with textbox method undo

Greetings,

I have a form with a file menu "Delete" which clears all selected text in a
textbox.

The issue being is that I want to be able to undo this transaction using
tetxbox.undo.

The delete procedure using textbox.text ="" OR textbox.clear() BOTH result
in the command textbox.CanUndo being FALSE.

How can I make this delete procedure work with an undo?

I am trying to replicate the functionality provided in wordpad where
selected text can be deleted and then the transaction can be undone.

Thanks
Rob