Mention what a missing :group does

* doc/lispref/customize.texi (Common Keywords): Document that
a missing :group reuses the group from the preceding item (bug#21601).

1 files changed, 7 insertions, 3 deletions

diff --git a/doc/lispref/customize.texi b/doc/lispref/customize.texi
index 14e6eb3ab25..de130d57d30 100644
--- a/doc/lispref/customize.texi
+++ b/doc/lispref/customize.texi
@@ -66,9 +66,13 @@ cause confusion.}
 
 @kindex group@r{, customization keyword}
 @item :group @var{group}
-Put this customization item in group @var{group}.  When you use
-@code{:group} in a @code{defgroup}, it makes the new group a subgroup of
-@var{group}.
+Put this customization item in group @var{group}.  If this keyword is
+missing from a customization item, it'll be placed in the same group
+as the previous customization item that had a @code{:group} spec (in
+the same file).
+
+When you use @code{:group} in a @code{defgroup}, it makes the new
+group a subgroup of @var{group}.
 
 If you use this keyword more than once, you can put a single item into
 more than one group.  Displaying any of those groups will show this