Tri-state kerning in Firefox involving /space (bug or feature?)

Adam Jagosz
Adam Jagosz Posts: 689
edited April 2018 in Font Technology
I have a problem with kerning in Firefox. I decided to give the letters with vertical caron negative kerning against round x-height letters (which works as expected), and then I thought it would be nice to include a slight negative kerning against space. The thing is—when I rely on browser defaults for font-feature-settings, Firefox applies the kerning for the first case but ignores the case with space. When I explicitly turn on kerning, space is kerned with the caron letters correctly. Which means the kerning for my font in Firefox can be: on, off, or ‘just a bit off’ >:)

In Chrome the space is not kerned at all even when kerning is explicitly enabled.

Everything works fine in Word, InDesign, Edge (which doesn't turn kerning on by default, so no tri-state experiments are possible).

I suppose this has to do with space being a multiscript character?


  • Thomas Phinney
    Thomas Phinney Posts: 2,807
    It might also be because some layout engines treat the space as a character that breaks the text run. I suspect that as a result they simply don’t process the space in OpenType layout, including kerning  :( 

    (I know for sure that one of Adobe’s layout engines do or at least formerly did this, a subject of some frustration for me.)
  • Khaled Hosny
    That sounds like a bug in Firefox and Chrome. I’m pretty sure their expected behavior is that if the font has any lookups that apply to space, then the optimization that splits words at space should be disabled.