Use BeforeInsertNodeAt to preprocess new nodes.
Use BeforeInsertNodeAt to preprocess new nodes.

The old code used the events provided by updater_domlistener, which made it so
that the DOM elements in the GUI tree would be updated *after* they are in the
DOM tree. This caused quite a bit of a slowdown. We now use BeforeInsertNodeAt
to process them *before* they get into the tree.

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