Cypress.on(...)'s undocumented parameter when registering app events' handlers

[vstreltsova-evinced]

Description of my task

For catching url-changes in my application I listen to the Cypress' app event called url:changed (more info here https://docs.cypress.io/api/cypress-api/catalog-of-events#App-Events):
Cypress.on('url:changed', urlChanged);
and my urlChanged-method is asynchronous.

I found an undocumented parameter when registering an event-handler - it's called async:
Cypress.on('url:changed', urlChanged, { async: true });
When I use it like above my urlChanged-method is executed synchronously. Seems in fact all the method's await's just started working after specifying that.

Questions

1. Is it correct that by specifying this async-parameter as true we get a synchronous execution of the event-handler method? Since there're no information about this parameter in the documentation, I'm not sure what behaviour to expect.
2. I found out the Cypress.on accepts additional options:

- there the EventEmitter2 library is involved. Is it correct that under the hood the Cypress uses this library? Can I rely on the library's documentation then? I found a description of the async-parameter in the library's documentation: https://github.com/EventEmitter2/EventEmitter2#emitteronevent-listener-options-objectboolean

3. If the async-parameter is valid to use for managing event-handlers' execution, probably it should be included to the Cypress' documentation?