How to use dash.callback Event input

Dash Python
1

IN this thread the OP has some code…

@app.callback(
    Output('google_markup', 'children'),
    [],
    [
        State('userButton', 'value'),
        State('sessionsButton', 'value')
    ],
    [
        Event('userButton', 'click'),
        Event('sessionsButton', 'click')]
)

I can’t find any documentation anywhere (including help(dash.callback)) about using an Event in a callback.

Is there some documentation anywhere?