[coldtea]

>CSS is more powerful than anything that popular native text editors can do

Which give even more credence to what the parent said: that "CSS isn't the right abstraction for styles in a text editor…".

We don't really need the "more power" in an editor, but we could use the less slugginess (and less conceptual overhead) than what CSS offer.

>Is it worth restricting an editor to only styles that don't influence block layout? For example, should it be impossible for a theme to make comment lines taller or shorter?

I'm pretty sure existing editors can do that today too, without CSS. Setting a different font size for comment lines for example.

[pcwalton]

If any editor has to restyle all lines, even lines that are off screen, and it supports declarative themes, then it must do the very same thing the browser does. And I suspect that any editor that does this styling will end up being slower than browsers are at this task, because of the sheer amount of optimization that has gone into browser styling at this point.