Polymer('paper-tabs', {
    
    /**
     * If true, ink effect is disabled.
     *
     * @attribute noink
     * @type boolean
     * @default false
     */
    noink: false,
    
    /**
     * If true, the bottom bar to indicate the selected tab will not be shown.
     *
     * @attribute nobar
     * @type boolean
     * @default false
     */
    nobar: false,
    
    activateEvent: 'down',
    
    nostretch: false,
    
    selectedIndexChanged: function(old) {
      var s = this.$.selectionBar.style;
      
      if (!this.selectedItem) {
        s.width = 0;
        s.left = 0;
        return;
      } 
      
      var w = 100 / this.items.length;
      
      if (this.nostretch || old === null || old === -1) {
        s.width = w + '%';
        s.left = this.selectedIndex * w + '%';
        return;
      }
      
      var m = 5;
      this.$.selectionBar.classList.add('expand');
      if (old < this.selectedIndex) {
        s.width = w + w * (this.selectedIndex - old) - m + '%';
      } else {
        s.width = w + w * (old - this.selectedIndex) - m + '%';
        s.left = this.selectedIndex * w + m + '%';
      }
    },
    
    barTransitionEnd: function() {
      var cl = this.$.selectionBar.classList;
      if (cl.contains('expand')) {
        cl.remove('expand');
        cl.add('contract');
        var s = this.$.selectionBar.style;
        var w = 100 / this.items.length;
        s.width = w + '%';
        s.left = this.selectedIndex * w + '%';
      } else if (cl.contains('contract')) {
        cl.remove('contract');
      }
    }
    
  });