code: function removeRemovedItems(uiContainer, optionsGroup) {
      const options = Array.prototype.slice.call(optionsGroup.children)
      let currentItemUi = uiContainer.firstElementChild
      while (currentItemUi) {
        if (options.indexOf(currentItemUi._option) > -1) {
          currentItemUi = currentItemUi.nextElementSibling
          continue
        }
  
        const itemToRemove = currentItemUi
        currentItemUi = currentItemUi.nextElementSibling
        uiContainer.removeChild(itemToRemove)
      }
    }
docs: Removes UI items from the UI that have been representing the options and option groups that have been removed from
  the provided container of options.
  
  @param {Element} uiContainer The element containing the elements reflecting the provided options and providing the
  UI for the options.
  @param {HTMLElement} optionsGroup The element containing the options for which this szn-options element is
  providing the UI.