>> +(defcustom describe-bindings-after-hook '(describe-bindings-outline)
>> +  "Hook run at the end of `describe-bindings'."
>> +  :type 'hook
>> +  :options '(describe-bindings-outline)
>> +  :group 'help
>> +  :version "28.1")
>
> What's the rationale for populating the hook by default?  That's not
> what we normally do: hooks are for Lisp programs to use, not for the
> core functionality to invoke itself.

This was an attempt of generalization.

>> +(defun describe-bindings-outline ()
>> +  "Hook to enable outlines in the output buffer of `describe-bindings'."
>
> First, this is not a hook.
>
> And second, if we want a feature whereby the buffer describing
> bindings could be put in Outline mode, why not offer a simple option
> for users to customize, not a hook for users to tweak?  Once again,
> having user options that accept only function values is
> user-unfriendly.

Function values are user-friendly when their defcustom provides
human-readable tags.

But in this case it's fine to have a simple option like in this patch: