Can anybody explain subplugins.json like I'm 5, please

I'm trying to add subplugins to my local plugin and understand that I have to create a subplugins.php file. However, I can't figure out what the correct/latest format is.I've foundMDL-83705but I'm just (more) confused.{"subplugintypes": {"assignsubmission": "submission","assignfeedback": "feedback"},"plugintypes": {"assignsubmission": "mod/assign/submission","assignfeedback": "mod/assign/feedback"}}In the example, from the ticket, what's the difference between 'subplugintypes' and 'plugintypes' (and why)?EDIT:I'm getting grief about a 'plugininfo' class but I can't find any documentation about what should be in there?