Flex-objects relations. Any examples?

Here it's stated that

"Flex objects can have relations to other Flex objects with few lines of code defining the relation"

Can we have any examples on creating these relations? One-to-one, one-to-many and many-to-many?

I got the same question.

Davay, did you manage to find it out yourself and want to share any experience?

There's a lack of documentation for the whole flex-objects part of Grav and I decided to wait some time for it to settle. And think about learning PHP deep enough to deal with it by myself ;)

Hm, thats a pitty! I think I need to use the database plugin for now, as I need a robust solution.