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(source) Virtual events are derived events: you can create virtual events yourself, and also combine normal events into one virtual. They are written as <<virtual event>>

When an event happens, Ev() can be used to collect some information about the event. Warning: Ev is a subroutine, not a method. You can only use it directly in the callback, not in the subroutine which is called by the callback. If you like to collect data within the called subroutine you have to play with XEvent.