Custom Add ons

Is it possible to create custom add ons for this like the front end submission add on?

If so, Is there any documentation about creating external add ons similar to how the official add ons were created?

I’ve attempted to follow the event modal creation patterns through registering my controller but am suspecting that class autoloader is built to only work with internal add ons by evidence on the phpdoc for extension_acknowledge() in Ai1ec_Registry_Object.

https://www.ads-software.com/plugins/all-in-one-event-calendar/