bug#35351: 27.0.50; Enable derived modes to run their own very-early 'change-major-mode-hook' code

[Richard Stallman]

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  > I forgot to mention the other hack solution which occurred to me,
  > which is for the library which defines the major mode to add its
  > own before-advice for that major mode function.

We have adopted the design principle that advice is for users to add,
and nothing else.

This is because developers investigating why a call to the function
foo doesn't work as expected will not think of the possibility that
foo has advice.

Thus, our design rule is that, if you want some code to be run before
or after calls to foo, add code to foo to run a hook.  This way, the
code for foo will show developers that a hook is called.
-- 
Dr Richard Stallman
President, Free Software Foundation (https://gnu.org, https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)