Created attachment 276102 [details] sample html font-feature-settings don't apply to space character. Please look at the sample.
Created attachment 276103 [details] Rendering WebKit Nightly r199279 png image
Created attachment 276104 [details] Rendering TextEdit.app png image
I'm having the same problem. I built a font that includes dots in the space and non-breaking space characters which can be activated using Stylistic Set 04. The dots display in other browsers but not in Safari. Live test here: https://dl.dropboxusercontent.com/u/10087441/Atlas%20Web%20Fonts%20wSpace%20160418/visible%20space.html We've noticed the same thing in other fonts where font-feature-settings: tnum; will not substitute the tabular space. Browsers: Safari: Version 9.1 (11601.5.17.1) Tech Preview: Version 9.1.1 (11601.6.15, 11602.1.27)
<rdar://problem/25831777>
Yeah, this is a pretty bad bug and is due to how we chop up text before we measure it. I really want to fix this, but unfortunately, there is no straightforward way to fix this quickly. I will do it as soon as I can.