stop the world and let me get off

svn: r17110

collects/teachpack/2htdp/scribblings/universe.scrbl

@@ -443,6 +443,16 @@ All @tech{MouseEvent}s are represented via strings:
 
 @item{
 
+@defproc[(STOP! [w (unsyntax @tech{WorldState})]) boolean?]{signals to
+DrScheme that the current world program should shut down. That is, any
+handler may return @scheme[(STOP! w)] provided @scheme[w] is a
+@tech{WorldState}. If it does, the state of the world becomes @scheme[w]
+but @scheme[big-bang] will close down all event handling.}
+
+}
+
+@item{
+
 @defform[(check-with world-expr?)
          #:contracts
          ([world-expr? (-> Any boolean?)])]{