How to find when a function/var has been added

[Przemysław Wojnowski]

Hello everybody,

What is the fastest way to find out since when a function/var is available in 
Emacs? Only through NEWS?

It's common case when one writes an elisp package and want to preserve 
compatibility with previous Emacs versions.

In Java it's very common to see in docs on classes/methods/fields "Since: n", 
where "n" is Java version. Wouldn't such information help in core Emacs libs 
too? What do you think?

Thanks,
Przemysław