You're seeing just the callback
handle_event, go back to Membrane.Element.Base module for more information.
handle_event( pad :: Membrane.Pad.ref_t(), event :: Membrane.Event.t(), context :: Membrane.Element.CallbackContext.Event.t(), state :: Membrane.Element.state_t() ) :: callback_return_t()
Callback that is called when event arrives.
Events may arrive from both sinks and sources. In filters by default event is forwarded to all sources or sinks, respectively.