diff --git a/lisp/ibuf-macs.el b/lisp/ibuf-macs.el
index 2f4d50d9a3e..2411f0588e3 100644
--- a/lisp/ibuf-macs.el
+++ b/lisp/ibuf-macs.el
@@ -198,8 +198,12 @@ operation is complete, in the form:
 ACTIVE-OPSTRING is a string which will be displayed to the user in a
 confirmation message, in the form:
  \"Really ACTIVE-OPSTRING x buffers?\"
-COMPLEX means this function is special; see the source code of this
-macro for exactly what it does.
+COMPLEX means this function is special; if COMPLEX is nil BODY
+evaluates once for each marked buffer, MBUF, with MBUF current
+and saving the point.  If COMPLEX is non-nil, BODY evaluates
+without requiring MBUF current.
+BODY define the operation; they are forms to evaluate per each
+marked buffer.
 
 \(fn OP ARGS DOCUMENTATION (&key INTERACTIVE MARK MODIFIER-P DANGEROUS OPSTRING ACTIVE-OPSTRING COMPLEX) &rest BODY)"
   (declare (indent 2) (doc-string 3))