docs: function register(val) {
        var content = void 0;
        var template = document.createElement('template');
        template.innerHTML = val;
        if (template.content) {
          content = template.content; // eslint-disable-line prefer-destructuring
        } else {
          content = document.createDocumentFragment();
          while (template.firstChild) {
            content.appendChild(template.firstChild);
          }
        }
        document.importNode(content, true);
      }