To copy HTML from one div to another, just use the DOM.

function copyHtml(source, destination) {

  var clone = source.ownerDocument === destination.ownerDocument

      ? source.cloneNode(true)

      : destination.ownerDocument.importNode(source, true);

  while (clone.firstChild) {

    destination.appendChild(clone.firstChild);

  }

}

For most apps, inSameDocument is always going to be true, so you can probably elide all the parts that function when it is false. If your app has multiple frames in the same domain interacting via JavaScript, you might want to keep it in.

If you want to replace HTML, you can do it by emptying the target and then copying into it:

function replaceHtml(source, destination) {

  while (destination.firstChild) {

    destination.removeChild(destination.firstChild);

  }

  copyHtml(source, destination);

}