Sort of a follow-up to #297 (comment):

I think a better option would be to add support for absolute line height to the style settings--that way, if one wants to avoid the "jitter", they can provide a round number for the line height themselves.

But this seems like it would also be useful for other applications, either because they allow their API consumers to specify line height in absolute units or because they resolve the units themselves (e.g. Blitz).

Currently you can work around this by just dividing the resolved absolute line height by the font size, so Parley can multiply it again (which is what Blitz does) but has the potential to introduce floating-point error and feels somewhat kludgey.