Thanks for the explanations, I never realized that concat was so
versatile (and I'm an emacs lover since 1983). Live and learn ...

Here is a suggested replacement for the documentation string (patch
attached). It produces

	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, etc. see ‘mapcar’.
	SEPARATOR and all values returned by FUNCTION must be accepted by ‘concat’.

--phs