function findCommonOffsetParent(element1, element2) {
    // This check is needed to avoid errors in case one of the elements isn't defined for any reason
    if (!element1 || !element1.nodeType || !element2 || !element2.nodeType) {
      return document.documentElement;
    }

    // Here we make sure to give as "start" the element that comes first in the DOM
    var order = element1.compareDocumentPosition(element2) & Node.DOCUMENT_POSITION_FOLLOWING;
    var start = order ? element1 : element2;
    var end = order ? element2 : element1;

    // Get common ancestor container
    var range = document.createRange();
    range.setStart(start, 0);
    range.setEnd(end, 0);
    var commonAncestorContainer = range.commonAncestorContainer;

    // Both nodes are inside #document

    if (element1 !== commonAncestorContainer && element2 !== commonAncestorContainer || start.contains(end)) {
      if (isOffsetContainer(commonAncestorContainer)) {
        return commonAncestorContainer;
      }

      return getOffsetParent(commonAncestorContainer);
    }

    // one of the nodes is inside shadowDOM, find which one
    var element1root = getRoot(element1);
    if (element1root.host) {
      return findCommonOffsetParent(element1root.host, element2);
    } else {
      return findCommonOffsetParent(element1, getRoot(element2).host);
    }
  }
Finds the offset parent common to the two provided nodes
@method
@memberof Popper.Utils
@argument {Element} element1
@argument {Element} element2
@returns {Element} common offset parent