Background areas are now neatly ignored from stacking

lib/timeline/Stack.js

@@ -49,7 +49,7 @@ exports.stack = function(items, margin, force) {
   // calculate new, non-overlapping positions
   for (i = 0, iMax = items.length; i < iMax; i++) {
     var item = items[i];
-    if (item.top === null) {
+    if (item.stack && item.top === null) {
       // initialize top position
       item.top = margin.axis;
 
@@ -59,7 +59,7 @@ exports.stack = function(items, margin, force) {
         var collidingItem = null;
         for (var j = 0, jj = items.length; j < jj; j++) {
           var other = items[j];
-          if (other.top !== null && other !== item && other.ignoreStacking == false && exports.collision(item, other, margin.item)) {
+          if (other.top !== null && other !== item && other.stack && exports.collision(item, other, margin.item)) {
             collidingItem = other;
             break;
           }

lib/timeline/component/item/BackgroundItem.js

@@ -34,13 +34,13 @@ function BackgroundItem (data, conversion, options) {
 
   Item.call(this, data, conversion, options);
 
-  this.ignoreStacking = true; // this is not used when stacking
   this.emptyContent = false;
 }
 
 BackgroundItem.prototype = new Item (null, null, null);
 
 BackgroundItem.prototype.baseClassName = 'item background';
+BackgroundItem.prototype.stack = false;
 
 /**
  * Check whether this item is visible inside given range

lib/timeline/component/item/Item.js

@@ -26,10 +26,10 @@ function Item (data, conversion, options) {
   this.left = null;
   this.width = null;
   this.height = null;
-
-  this.ignoreStacking = false;
 }
 
+Item.prototype.stack = true;
+
 /**
  * Select current item
  */