Comment by kevinb7

My limited understanding of MathJax is that it uses the browser to measure glyphs. KaTeX on the other hand includes metrics for many of its glyphs. Where things get a little tricky is i18n. There are many languages which our current fonts don't cover and thus we have no metrics for them (we make some educated guess about some unicode ranges). It would be really nice if browsers implemented a Font Metrics API, unfortunately efforts to do so appear stalled at the moment.