[Self answered, but posted as it may be useful to others]
Is there a way to have one form "replace" another? I want to have a login form, and
then once they have logged in, to change the "main" form to be the working form.
This would sort of be a "stack" of forms, as I'd want to be able to return later.
At the moment, if I click my login button and do the NewForm.ShowModal, the form
appears overlaid on the main form. I realise I can control this a bit, but the
original is there still.
Okay, I just realised, while about to quote from the help (the usage for TForm is
particularly good), that this is entirely possible. Self.Hide and using the OnClose
to show it again.