bug#35710: 26.1; incomplete mapconcat description string

[Noam Postavsky]

phs <phs@lsv.fr> writes:

> In my v26.1, the description string for mapconcat is
>
>    mapconcat is a built-in function in ‘src/fns.c’.
>
>    (mapconcat FUNCTION SEQUENCE SEPARATOR)
>
>    Apply FUNCTION to each element of SEQUENCE, and concat the results as
> strings.
>    In between each pair of results, stick in SEPARATOR.  Thus, " " as
>    SEPARATOR results in spaces between the values returned by FUNCTION.
>    SEQUENCE may be a list, a vector, a bool-vector, or a string.
>
> The description does not say what is accepted for SEPARATOR, it only
> gives an example.

It mentions concat, which is what determines what is acceptable.  I
agree it could be made more explicit though.