1 files changed, 24 insertions, 0 deletions
diff --git a/doc/lispref/variables.texi b/doc/lispref/variables.texi
index b7b4f56212f..aa308348051 100644
--- a/doc/lispref/variables.texi
+++ b/doc/lispref/variables.texi
@@ -2695,6 +2695,30 @@ terminal-parameter            window-point
 keymap-parent                 window-start
 match-data                    default-value
 @end smallexample
+
+@item
+A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])},
+where @var{subplace} is itself a valid generalized variable whose
+current value is a string, and where the value stored is also a
+string.  The new string is spliced into the specified part of the
+destination string.  For example:
+
+@example
+(setq a (list "hello" "world"))
+     @result{} ("hello" "world")
+(cadr a)
+     @result{} "world"
+(substring (cadr a) 2 4)
+     @result{} "rl"
+(setf (substring (cadr a) 2 4) "o")
+     @result{} "o"
+(cadr a)
+     @result{} "wood"
+a
+     @result{} ("hello" "wood")
+@end example
+
+@c FIXME?  Also 'eq'? (see gv.el)
 @end itemize
 
 @noindent