>
> 1) It calls the specified object's to_proc() method.  And Symbol#to_proc
> is defined like this:
>

Small note, and some history:

This was originally introduced in ActiveSupport, where that was in fact the
definition. But performance was terrible. It was added to 1.8.7 & 1.9, but
is implemented in C, and is a bit more efficient. The semantics are the same
though.