From rsc by way of quanstro:

"from russ.  if a window is deleted with Del in the tag, and a new
window is moved in to replace it, then warp the mouse to Del.  this
facilliates the common case of deleting a bunch of windows at the same
time.  the theory is that the random pointer location in the newly
moved window wouldn't be useful anyway."

Reference: /n/sources/patch/applied/acme-warp
Date: Mon Aug 12 09:29:33 CES 2013
Signed-off-by: sstallion@gmail.com

--- /sys/src/cmd/acme/cols.c	Mon Aug 12 09:29:05 2013
+++ /sys/src/cmd/acme/cols.c	Mon Aug 12 09:29:02 2013
@@ -111,7 +111,7 @@
 colclose(Column *c, Window *w, int dofree)
 {
 	Rectangle r;
-	int i;
+	int i, didmouse, up;
 
 	/* w is locked */
 	if(!c->safe)
@@ -125,7 +125,7 @@
 	w->tag.col = nil;
 	w->body.col = nil;
 	w->col = nil;
-	restoremouse(w);
+	didmouse = restoremouse(w);
 	if(dofree){
 		windelete(w);
 		winclose(w);
@@ -137,6 +137,7 @@
 		draw(screen, r, display->white, nil, ZP);
 		return;
 	}
+	up = 0;
 	if(i == c->nw){		/* extend last window down */
 		w = c->w[i-1];
 		r.min.y = w->r.min.y;
@@ -144,10 +145,15 @@
 	}else{			/* extend next window up */
 		w = c->w[i];
 		r.max.y = w->r.max.y;
+		up = 1;
 	}
 	draw(screen, r, textcols[BACK], nil, ZP);
-	if(c->safe)
+	if(c->safe){
 		winresize(w, r, FALSE);
+		USED(up);
+		if(!didmouse)
+			movetodel(w);
+	}
 }
 
 void
--- /sys/src/cmd/acme/fns.h	Mon Aug 12 09:29:08 2013
+++ /sys/src/cmd/acme/fns.h	Mon Aug 12 09:29:06 2013
@@ -19,10 +19,11 @@
 char*	getname(Text*, Text*, Rune*, int, int);
 void	scrsleep(uint);
 void	savemouse(Window*);
-void	restoremouse(Window*);
+int	restoremouse(Window*);
 void	clearmouse(void);
 void	allwindows(void(*)(Window*, void*), void*);
 uint loadfile(int, uint, int*, int(*)(void*, uint, Rune*, int), void*);
+void	movetodel(Window*);
 
 Window*	errorwin(Mntdir*, int);
 Window*	errorwinforwin(Window*);
--- /sys/src/cmd/acme/util.c	Mon Aug 12 09:29:12 2013
+++ /sys/src/cmd/acme/util.c	Mon Aug 12 09:29:10 2013
@@ -366,12 +366,18 @@
 	mousew = w;
 }
 
-void
+int
 restoremouse(Window *w)
 {
-	if(mousew!=nil && mousew==w)
+	int did;
+
+	did = 0;
+	if(mousew!=nil && mousew==w){
 		moveto(mousectl, prevmouse);
+		did = 1;
+	}
 	mousew = nil;
+	return did;
 }
 
 void
--- /sys/src/cmd/acme/wind.c	Mon Aug 12 09:29:17 2013
+++ /sys/src/cmd/acme/wind.c	Mon Aug 12 09:29:14 2013
@@ -84,6 +84,34 @@
 }
 
 int
+delrunepos(Window *w)
+{
+	int n;
+	Rune rune;
+	
+	for(n=0; n<w->tag.file->nc; n++) {
+		bufread(w->tag.file, n, &rune, 1);
+		if(rune == ' ')
+			break;
+	}
+	n += 2;
+	if(n >= w->tag.file->nc)
+		return -1;
+	return n;
+}
+
+void
+movetodel(Window *w)
+{
+	int n;
+	
+	n = delrunepos(w);
+	if(n < 0)
+		return;
+	moveto(mousectl, addpt(frptofchar(&w->tag, n), Pt(4, w->tag.font->height-4)));
+}
+
+int
 winresize(Window *w, Rectangle r, int safe)
 {
 	Rectangle r1;