Keynav skips masked boxes

internal/system/hierarchy.go

@@ -287,13 +287,26 @@ func (this *Hierarchy) considerMaskingParents (box anyBox) anyBox {
 	return box
 }
 
+func (this *Hierarchy) isMasked (box anyBox) bool {
+	parent := box.getParent()
+	for {
+		parentBox, ok := parent.(anyBox)
+		if !ok { break }
+		if parent.masks() {
+			return true
+		}
+		parent = parentBox.getParent()
+	}
+	return false
+}
+
 func (this *Hierarchy) focusNext () {
 	found   := !this.anyFocused()
 	focused := false
 	this.propagateAlt(func (box anyBox) bool {
 		if found {
 			// looking for the next box to select
-			if box.canBeFocused() {
+			if box.canBeFocused() && !this.isMasked(box) {
 				// found it
 				this.focus(box)
 				focused = true