unmark(opt) {
    this.opt = opt;
    let sel = this.opt.element ? this.opt.element : '*';
    sel += '[data-markjs]';
    if (this.opt.className) {
      sel += `.${this.opt.className}`;
    }
    this.log(`Removal selector "${sel}"`);
    this.iterator.forEachNode(NodeFilter.SHOW_ELEMENT, node => {
      this.unwrapMatches(node);
    }, node => {
      const matchesSel = DOMIterator.matches(node, sel),
        matchesExclude = this.matchesExclude(node);
      if (!matchesSel || matchesExclude) {
        return NodeFilter.FILTER_REJECT;
      } else {
        return NodeFilter.FILTER_ACCEPT;
      }
    }, this.opt.done);
  }
Removes all marked elements inside the context with their HTML and
normalizes the parent at the end
@param  {Mark~commonOptions} [opt] - Optional options object without each,
noMatch and acrossElements properties
@access public