code: function upTo(el, tagName) {
    tagName = tagName.toLowerCase();
  
    while (el && el.parentNode) {
      el = el.parentNode;
      if (el.tagName && el.tagName.toLowerCase() == tagName) {
        return el;
      }
    }
    // Many DOM methods return null if they don't
    // find the element they are searching for
    // It would be OK to omit the following and just
    // return undefined
    return null;
  }
docs: Find first ancestor of el with tagName or undefined if not found