Re: The dynamic-docstring-function property

[Chong Yidong <cyd@gnu.org>]

Stefan Monnier <monnier@IRO.UMontreal.CA> writes:

>> Is there any reason only `documentation' uses this property, and not
>> `documentation-property' or `face-documentation'?
>
> The reason is that there hasn't been a need for it.

I'm trying to document the feature now, and I don't understand why this
feature had to be introduced in the first place.  Isn't it redundant
with the pre-existing `function-documentation' feature?

As noted in the Lisp manual,

 -- Function: documentation function &optional verbatim

 ...

 If FUNCTION is a symbol, this function first looks for the
 `function-documentation' property of that symbol; if that has a
 non-nil value, the documentation comes from that value (if the value
 is not a string, it is evaluated).

Because a non-string value is evaluated, the dynamic-docstring-function
stuff can be accomplished by setting the function-documentation property
to the value `(foo ,old-docstring) where `foo' is your processing
function.