setActiveItem (index) {
    if (!this._items[index]) {
      throw new Error('CSS-Modal: Invalid index "' + index + '"!');
    }

    var content = this._items[index].innerHTML;
    var img = new Image();
    var referenceImage;

    this._detailView.innerHTML = content;

    // Position for loading indicator and hide content
    this.Helpers.trigger('cssmodal:resize', this._activeElement);
    this.Helpers.removeClass(this._detailView, 'is-active');

    // Set a caption for the modal
    this.setCaption(this._items[index].getAttribute('data-caption'));

    // Load the original image, if we are in a gallery
    if (this._activeElement.getAttribute('class').indexOf('modal--gallery') !== -1) {
      referenceImage = this._detailView.getElementsByTagName('img')[0];

      if (referenceImage.parentNode.getAttribute('data-iframe') !== null) {
        img = document.createElement('iframe');
        img.src = referenceImage.getAttribute('data-src-fullsize');
        img.setAttribute('webkitallowfullscreen', true);
        img.setAttribute('mozallowfullscreen', true);
        img.setAttribute('allowfullscreen', true);

      } else {
        img.src = referenceImage.getAttribute('data-src-fullsize');
        img.alt = referenceImage.getAttribute('alt');
      }

      // Reposition and show
      this.Helpers.on('load', img, () => {
        this.Helpers.addClass(this._detailView, 'is-active');
        this.Helpers.trigger('cssmodal:resize', this._activeElement);
      });

      referenceImage.parentNode.insertBefore(img, referenceImage);
      referenceImage.parentNode.removeChild(referenceImage);

      this._detailView.style.width = 'auto';
      this._detailView.style.height = 'auto';
    }
  }
Shows the full content of the designated item
@param {Number} index The index of the item to show