(Defining Abbrevs): Mention `define-abbrev' 'force

value for system-flag argument.

1 files changed, 4 insertions, 1 deletions

diff --git a/lispref/abbrevs.texi b/lispref/abbrevs.texi
index 52b3dfe1ad6..56d08c7393b 100644
--- a/lispref/abbrevs.texi
+++ b/lispref/abbrevs.texi
@@ -165,7 +165,10 @@ returns @code{nil}, @code{expand-abbrev} also returns @code{nil}, as
 if expansion had not really occurred.
 
 If @var{system-flag} is non-@code{nil}, that marks the abbrev as a
-``system'' abbrev with the @code{system-type} property.
+``system'' abbrev with the @code{system-type} property.  Unless
+@var{system-flag} has the value @code{force}, a ``system'' abbrev will
+not overwrite an existing definition for a non-``system'' abbrev of the
+same name.
 
 Normally the function @code{define-abbrev} sets the variable
 @code{abbrevs-changed} to @code{t}, if it actually changes the abbrev.