MDL-47494 ddwtos: Hilight drop target, and use YUI dd groups.

question/type/ddwtos/styles.css

@@ -36,10 +36,15 @@
     -moz-box-shadow: 3px 3px 4px #000;
     -webkit-box-shadow: 3px 3px 4px #000;
     box-shadow: 3px 3px 4px #000;
-    /* For IE 8 */
-    -ms-filter: "progid:DXImageTransform.Microsoft.Shadow(Strength=4, Direction=135, Color='#000000')";
     /* For IE 5.5 - 7 */
     filter: progid:DXImageTransform.Microsoft.Shadow(Strength=4, Direction=135, Color='#000000');
+    /* For IE 8 */
+    -ms-filter: "progid:DXImageTransform.Microsoft.Shadow(Strength=4, Direction=135, Color='#000000')";
+}
+
+.que.ddwtos .drop.yui3-dd-drop-over.yui3-dd-drop-active-valid {
+    border-color: #0a0;
+    box-shadow: 0 0 5px 5px rgba(255, 255, 150, 1);
 }
 
 .que.ddwtos .notreadonly .drag {

question/type/ddwtos/yui/dd/dd.js

@@ -206,6 +206,7 @@ YUI.add('moodle-qtype_ddwtos-dd', function(Y) {
             var group = this.get_group(drag);
             var dd = new Y.DD.Drag({
                 node: drag,
+                groups: [this.get_group(drag)],
                 dragMode: 'point'
             }).plug(Y.Plugin.DDConstrained, {constrain2node: this.selectors.top_node()});
         },
@@ -214,7 +215,8 @@ YUI.add('moodle-qtype_ddwtos-dd', function(Y) {
         },
         make_drop_zone : function (drop) {
             var dropdd = new Y.DD.Drop({
-                node: drop});
+                node: drop,
+                groups: [this.get_group(drop)] });
             dropdd.on('drop:hit', function(e) {
                 var drag = e.drag.get('node');
                 var drop = e.drop.get('node');