_showElement(element: HTMLElement) {
    if (this.options.class.visible) {
      element.classList.add(this.options.class.visible);
    }
    if (element.classList.contains(this.options.class.hidden)) {
      element.classList.remove(this.options.class.hidden);
      this.hidden--;

      if (typeof this.options.onVisible === 'function') {
        this.options.onVisible(element);
      }
    }
    if (this.options.hiddenAttr) {
      element.removeAttribute('hidden');
    }

    // If we need to mark it:
    // remove all <mark> tags
    // add new <mark> tags around the text
    if (this.options.mark) {
      element.innerHTML = element.innerHTML.replace(/<\/?mark>/g, '');
      if (this.searchString.length) {
        element.innerHTML = element.innerHTML.replace(
          this._regex,
          '<mark>$1</mark>'
        );
      }
    }
  }
Show an element
@function _showElement
@param  {HTMLElement} element the element to show
@memberOf holmes
@private