diff --git a/attachments.scad b/attachments.scad
index 14c252b..4be6ffa 100644
--- a/attachments.scad
+++ b/attachments.scad
@@ -464,7 +464,6 @@ module edge_mask(edges=EDGES_ALL, except=[]) {
 		$attach_anchor = anch;
 		$attach_norot = true;
 		$tags = "mask";
-		length = sum(vmul($parent_size, [for (x=vec) x?0:1]))+0.1;
 		rotang =
 			vec.z<0? [90,0,180+vang(point2d(vec))] :
 			vec.z==0 && sign(vec.x)==sign(vec.y)? 135+vang(point2d(vec)) :
@@ -475,6 +474,46 @@ module edge_mask(edges=EDGES_ALL, except=[]) {
 }
 
 
+// Module: corner_mask()
+// Usage:
+//   corner_mask([corners], [except]) ...
+// Description:
+//   Takes a 3D mask shape, and attaches it to the given corners, with the appropriate
+//   orientation to be `diff()`ed away.  The 3D corner mask shape should be designed to
+//   mask away the X+Y+Z+ octant.
+// Arguments:
+//   corners = Edges to mask.  See the docs for [`corners()`](edges.scad#corners) to see acceptable values.  Default: All corners.
+//   except = Edges to explicitly NOT mask.  See the docs for [`corners()`](edges.scad#corners) to see acceptable values.  Default: No corners.
+// Side Effects:
+//   Sets `$tags = "mask"` for all children.
+// Example:
+//   diff("mask")
+//   cube(100, center=true)
+//       corner_mask([TOP,FRONT],LEFT+FRONT+TOP)
+//           difference() {
+//               translate(-0.01*[1,1,1]) cube(20);
+//               translate([20,20,20]) sphere(r=20);
+//           }
+module corner_mask(corners=CORNERS_ALL, except=[]) {
+	assert($parent_size != undef, "No object to attach to!");
+	corners = corners(corners, except=except);
+	vecs = [for (i = [0:7]) if (corners[i]>0) CORNER_OFFSETS[i]];
+	for (vec = vecs) {
+		vcount = (vec.x?1:0) + (vec.y?1:0) + (vec.z?1:0);
+		assert(vcount == 3, "Not an edge vector!");
+		anch = find_anchor(vec, $parent_size.z, point2d($parent_size), size2=$parent_size2, shift=$parent_shift, offset=$parent_offset, anchors=$parent_anchors, geometry=$parent_geom, two_d=$parent_2d);
+		$attach_to = undef;
+		$attach_anchor = anch;
+		$attach_norot = true;
+		$tags = "mask";
+		rotang = vec.z<0?
+			[  0,0,180+vang(point2d(vec))-45] :
+			[180,0,-90+vang(point2d(vec))-45];
+		translate(anch[1]) rot(rotang) children();
+	}
+}
+
+
 // Module: tags()
 // Usage:
 //   tags(tags) ...
diff --git a/edges.scad b/edges.scad
index f6227f0..c434455 100644
--- a/edges.scad
+++ b/edges.scad
@@ -35,7 +35,6 @@
 //   }
 //   module corner_cube(size=20, txtsize=3, corners="ALL") {
 //       corner_set = _corner_set(corners);
-//       echo(corners=corners, corner_set=corner_set);
 //       lbl = is_string(corners)? [str("\"",corners,"\"")] : concat(
 //            corners.z>0? ["TOP"] : corners.z<0? ["BTM"] : [],
 //            corners.y>0? ["BACK"] : corners.y<0? ["FWD"] : [],
@@ -281,7 +280,6 @@ function _corner_set(v) =
 				str(v, " must be a vector, corner array, or one of ", valid_values)
 			) v
 		) :
-		echo("A", v=v, v2=v2, [for (i=[0:2]) !v[i] || (v[i]==v2[i])])
 		all([for (i=[0:2]) !v[i] || (v[i]==v2[i])])
 	)? 1 : 0
 ];
@@ -372,13 +370,13 @@ function _corner_set(v) =
 // Example: All corners around the bottom or front faces, except those on the bottom-front edge.
 //   corners([BOTTOM,FRONT], except=BOTTOM+FRONT)
 function corners(v, except=[]) =
-	(is_string(v) || is_corner_array(v))? corners([v], except=except) :
-	(is_string(except) || is_corner_array(except))? corners(v, except=[except]) :
+	(is_string(v) || is_vector(v) || is_corner_array(v))? corners([v], except=except) :
+	(is_string(except) || is_vector(except) || is_corner_array(except))? corners(v, except=[except]) :
 	except==[]? normalize_corners(sum([for (x=v) _corner_set(x)])) :
-	normalize_corners(
-		normalize_corners(sum([for (x=v) _corner_set(x)])) -
-		sum([for (x=except) _corner_set(x)])
-	);
+	let(
+		a = normalize_corners(sum([for (x=v) _corner_set(x)])),
+		b = normalize_corners(sum([for (x=except) _corner_set(x)]))
+	) normalize_corners(a - b);
 
 
 CORNER_OFFSETS = [   // Array of XYZ offsets to each corner.
diff --git a/version.scad b/version.scad
index aa19ebb..72e5530 100644
--- a/version.scad
+++ b/version.scad
@@ -8,7 +8,7 @@
 //////////////////////////////////////////////////////////////////////
 
 
-BOSL_VERSION = [2,0,122];
+BOSL_VERSION = [2,0,123];
 
 
 // Section: BOSL Library Version Functions