code: function(index, item)
  	{
  		var length = this.length;
  		
  		var replaced = this.source[index];
  		this.__updateBindings(replaced, false);
  		
  		this.source[index] = item;
  		this.__updateBindings(item);
  		
  		if (this.length > length)
  		{
  			this.dispatchEvent(new conbo.ConboEvent(conbo.ConboEvent.ADD));
  			this.dispatchChange('length');
  		}
  		
  		this.dispatchEvent(new conbo.ConboEvent(conbo.ConboEvent.CHANGE, {item:item}));
  		
  		return replaced;
  	}
docs: Add (or replace) item at given index with the one specified,
  similar to array[index] = value;