docs: function(elem, f) {
     // console.log("in onAppend, elem: "+elem);
    var observer = new MutationObserver(function(mutations, me) {
        //console.log("in mutationObserver, me: "+me);
        mutations.forEach(function(m) {
          console.log(m);
          if (m.addedNodes.length) {
              f(m.target, m.addedNodes)
          }
      })
    })
    observer.observe(elem, {childList: true})
  }