# Guard (filter, event)

A filter that covers its child with a striped shadow. On the first click, the guard is removed, exposing and activating the child. If the mouse moves out of the guarded area, the guard returns.

Behavior
  On down-click, the shadow becomes recessed; restores the raised shadow on up-click or chord-abort, and generates an event if the mouse is still within the button on the up-click.
Shape
  The shape of its child plus the shadow.
Notes
  A guard is often used around a component whose action has has potentially serious side-effects; e.g., `(Button "Delete")`, `(Boolean "Override")`.