Understand how plugins work

Hello,
I'm trying to understand how V3 plugins work.
I think there is a lot of possibility with that, but the documentation is very poor (this is not a reproach, I understand that all this takes time).

So I'm looking the existing plugins code.

But, even with documentation, I don't understand much.

For example, what is it exactly :
cursor.element ?
cursor.element.type ? When I try with console.log(cursor.element.type); I have always "92" for result.
cursor.segment ?
Element.CHORD ? Same thing, I have always 92.
cursor.element.notes ? I have "[object Object]" as result.

Thanks for your help.