One of the most annoying things in web development is when you have a lot of DOM operations to do, and it creates jank. We have web workers for doing lots of things in other processes... except DOM. React and others bypass it by doing everything in a virtual DOM, but in reality it makes things stupid slow because it's a DOM-like api rewritten in JS.
What we need is real DOM operations in web workers. It's understandable why we don't, but you don't have to do DOM operations on the main document. Allow DOM operations on a separate temporary document. The worker would message a DOM object back to the main process where you'd adopt the DOM object to the main document before insertion. This is DOM level 1 stuff.
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