The new DOM mutation methods are excellently great, but I would like to request the addition of one more function: swap.

Particularly for DOM diffing (turning one element into another) where the operations are removals, insertions and relocations, as well as "collection" relocations (moving a sequence of elements up/down in their container) a swap() operation will greatly improve legibility as well as writability.

Compare these two DOM fragments:

A:

<figure>
  <!--image-->
  <img...>
  <!-- guide text -->
  <figcaption>text</figcaption>
<figure>

B:

<figure>
  <!-- guide text -->
  <figcaption>text</figcaption>
  <!--image-->
  <img...>
<figure>

Turning A into B (as a diff, or because a user did something that was equivalent to a drag operation on the first two or last two non-Text nodes) using a .swap() operation would be a two line constructions:

  figure.swap(1,5); // or figure.swap(commentElement1, commentElement2)
  figure.swap(2,6); // or figure.swap(imgelement, figCaptionElement)

This code would be preferable to having to relocate elements using inserts, where each insert must be followed by checks to see whether a relocation now requires an insert, or an append because the next swap can be performed.

It would also reduce the number of DOM mutation events being generated for a swap from two events that are either the same (two inserts) or different (an insert and an append) to a single event that always represents a swap.