rulerView(_:shouldMove:)
Requests permission for aRulerView to move aMarker.
Declaration
func rulerView(_ ruler: NSRulerView, shouldMove marker: NSRulerMarker) -> BoolDiscussion
If the client returns true the ruler view allows the user to move the marker; if the client returns false the marker doesn’t move.
The user’s ability to move a marker is typically set on the marker itself, using NSRulerMarker’s isMovable method. You should use this client view method only when the marker’s movability can vary depending on a variable condition (for example, if graphic items can be locked down to prevent them from being inadvertently moved).