Windows allows only one caret per message queue. To add a caret to a control, handle the WM_SETFOCUS message, or the GotFocus event, or override OnGotFocus if you're writing a custom control, and call CreateCaret from the message or event handler. You should also handle WM_KILLFOCUS, LostFocus or OnLostFocus and call DestroyCaret. You will also need to call ShowCaret to make the caret visible, and SetCaretPos to set its position.
