code: function addSentinels(container, className, stickySelector = STICKY_SELECTOR) {
    return Array.from(container.querySelectorAll(stickySelector)).map((stickyElement) => {
      const sentinel = document.createElement('div');
      const stickyParent = stickyElement.parentElement;
  
      // Apply styles to the sticky element
  
      stickyElement.style.cssText = `
        position: -webkit-sticky;
        position: sticky;
      `;
  
      // Apply default sentinel styles
  
      sentinel.classList.add(ClassName.SENTINEL, className);
  
      Object.assign(sentinel.style,{
        left: 0,
        position: 'absolute',
        right: 0,
        visibility: 'hidden',
      });
  
      switch (className) {
        case ClassName.SENTINEL_TOP: {
          stickyParent.insertBefore(sentinel, stickyElement);
  
          // Apply styles specific to the top sentinel
  
          Object.assign(
            sentinel.style,
            getSentinelPosition(stickyElement, sentinel, className),
            { position: 'relative' },
          );
  
          break;
        }
  
        case ClassName.SENTINEL_BOTTOM: {
          stickyParent.appendChild(sentinel);
  
          // Apply styles specific to the bottom sentinel
  
          Object.assign(sentinel.style, getSentinelPosition(stickyElement, sentinel, className));
  
          break;
        }
      }
  
      return sentinel;
    });
  }
docs: Add sticky sentinels
  
  @param {Element|HTMLDocument} container
  @param {String} className
  @param {string} stickySelector     The CSS selector applied to the sticky DOM elements
  @returns {Array<Element>}