Listen registers an EventListener and starts a loop in a goroutine, which listens for new events (via PushEvent) and calls the listen function with them.

PushEvent adds a new event to the event channel, which something else can listen for and act on.

Shutdown sends a message to the shutdown channel, which would end any Listen goroutine.

command key.

control key.

These are key modifiers.

option key.

shift key.

An Event is a record of something that happened with user input.

An EventListener is a function which receives an event.