The flags in effect at the mouse-down event that started the current tracking session.
- macOS 10.0+
mouse method obtains these flags by sending a
modifier message to the event passed into
mouse. Use this property if you want to access these flags. This property is valid only during tracking; it isn’t useful if the target of the receiver initiates another tracking loop as part of its action method (as a cell that pops up a pop-up list does, for example).