> You're trying all sorts of hacks here, because the fundamental issue is that your data structure is the dom and css styling, so everything that other text editors would attach as few byte metadata you used to put in the dom.
That's part of the issue, yes. (The other, and more important, part of the issue is that CSS restyling has to occur in order for the browser to determine the changes that need to be applied to the render tree.) Note that the problem you describe has nothing to do with whether the text is off screen or not.
> Which means a simple threeliner that would be a couple of bytes in a proper designed editor, becomes the following beast in atom.
This is a misleading way to describe it, because the in-memory representation is compressed. Most of the identifiers in the DOM are compressed down to a single pointer, so they're treated as integers and only serialized when necessary. The objects are threaded together into a doubly linked tree, so the textual DOM doesn't actually live anywhere most of the time.
It's as if you took Vim's internal data structures and dumped them out into JSON. They'd be equally bloated and verbose in that format. That doesn't say anything about how efficient Vim is.
The one issue that does matter here is that the styles are currently stored as strings. It's a frequent bottleneck. There is a proposed Typed CSSOM standard [1] that is designed to address this problem. Note, again, that this has nothing to do with whether rendering happens offscreen or not.
[1]: https://drafts.css-houdini.org/css-typed-om-1/
