bug#44225: This variable was introduced, or its default value was changed, in ...

[積丹尼 Dan Jacobson]

describe-variable shows:

   xxxx.... is a variable defined in ‘yyyy.....el’.
   Its value is X
   Original value was Y

     You can customize this variable.

   This variable was introduced, or its default value was changed, in
   version ZZZ of Emacs.

Actually you could separately reveal:
Date/version when introduced.
Date/version when default value was changed.
Date/version when function guts last updated, or at least the
date/version of .el that it lives in.
etc.