Emacs 25.1 obsoletes a variable
isearch-word and recommends to use the new
isearch-regexp-function instead. Because Emacs 24 does not have the new variable, I can't just replace it like:
What's the best way to support both Emacs 24 and Emacs 25?
I don't want to just suppress the warning with
with-no-warnings, which is already answered here: "How to avoid obsolete warning when defining a compatibility alias?"