bug#40215: [PATCH 3/4] doc: Document default delimiter of string-join.

* doc/ref/api-data.texi (String Constructors): Document default
delimiter of the string-join function.
---
 doc/ref/api-data.texi | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/doc/ref/api-data.texi b/doc/ref/api-data.texi
index a6b09c478..3dd5109c4 100644
--- a/doc/ref/api-data.texi
+++ b/doc/ref/api-data.texi
@@ -3183,9 +3183,10 @@ produce the corresponding string element.  The order in which
 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
 Append the string in the string list @var{ls}, using the string
 @var{delimiter} as a delimiter between the elements of @var{ls}.
-@var{grammar} is a symbol which specifies how the delimiter is
-placed between the strings, and defaults to the symbol
-@code{infix}.
+@var{delimiter} defaults to @w{@samp{ }}, that is, strings in @var{ls}
+are appended with the space character in between them.  @var{grammar} is
+a symbol which specifies how the delimiter is placed between the
+strings, and defaults to the symbol @code{infix}.
 
 @table @code
 @item infix
-- 
2.25.1