Questions for the OptionSet event

Hi,

The OptionSet event has been introduced in 7.4.786, which looks useful.
I am trying to understand the behavior and I have found 2 questions now.

#1
For example,
set number
let &number = 1
generates the event, but
call setwinvar(0, '&number', 1)
does not. Why?

#2
diffthis and diffoff
generate the event only for scrollopt option.
How about other options like diff, scrollbind, cursorbind, wrap, foldmethod, and foldcolumn?

Thank you for your help.

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