All form controls signal the following dependency notifications:

- `#entered` - when the pen is pressed in the control's bounds.
- `#selected` - when the pen is lifted in the control's bounds.
- `#exited` - when the pen is lifted outside the control's bounds.

## Button

The aspect for a Button is the selector to be sent to the parent Application when the button is pressed. If the aspect is nil, no notification is sent when the button is pressed (the button still receives #entered, #selected, and #exited dependency events).

## Fields

Fields receive a #height dependency event when their height changes.