[pdkl95]

> Is it worth restricting an editor to only styles that don't influence block layout?

That includes font-* and many other attributes that affect text rendering. It isn't possible to know the length of a line of text without computing most of the text layout in modern font rendering. Font family/size/variant, weight, kerning, vertical hinting, traditional horizontal hinting, and LCD subpixel hinting all influence character positions at 1/256 pixel resolution. I highly recommend this[1] paper for a good overview of how this works, which includes an analysis of why Microsoft's older font handling caused serious layout issues (cumulative x-length error) due to over-hinting that forced glyphs onto the pixel grid.

> editors

Monospace fonts usually let you ignore most of these issues, but some (crazy?) people program with proportional fonts[2], and we can't actually ignore Unicode...

(I just use an 80/20 solution: fast - and predictable - Terminus and Dina bitmap fonts most of the time, and let Unicode distort the layout with other stuff as needed)

[1] http://www.antigrain.com/research/font_rasterization/index.h...

[2] https://news.ycombinator.com/item?id=1056683