Parametrized notification - question about the concept

Hi,

I am playing around with parametrized notifications (handler calls) and I have came to the following questions:

1/ Is it documented somewhere? I did not find anything about the subject in official docs only several issues on github (e.g. https://github.com/ansible/ansible/issues/4853#issuecomment-28719258). So please forgive me that I am only guessing.

2/ I have not found any valid reason to parametrize a notification with role variable only. Is there any? I am confused by this kind of behavior.

To be clear I am trying to notify a handler named client-handler-something and that something is stored as a variable. The task that notifies an appropriate handler may look as follows.

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