code: function isFixed(element) {
      var nodeName = element.nodeName;
  
      if (nodeName === 'BODY' || nodeName === 'HTML') {
        return false;
      }
  
      if (getStyleComputedProperty(element, 'position') === 'fixed') {
        return true;
      }
  
      var parentNode = getParentNode(element);
  
      if (!parentNode) {
        return false;
      }
  
      return isFixed(parentNode);
    }
docs: Check if the given element is fixed or is inside a fixed parent
  @method
  @memberof Popper.Utils
  @argument {Element} element
  @argument {Element} customContainer
  @returns {Boolean} answer to "isFixed?"