Created attachment 474665 [details] rendering in safari, firefox, chrome Thanks Peter for the report. There is another interesting difference. The way the coloring is done. <p>The dog <span style="color: red;">f</span>led.</p> Safari: Ligature: NO, Color: red on f Firefox: Ligature: YES, Color: red on f Chrome: Ligature: YES, Color: red on both f and l

Thank you Karl for that interesting addition. A little more context (ha). The ligature is a single glyph in the font, so rendering half of it in a different colour wouldn't normally be supported by the font itself. You can see in the Firefox screenshot how colouring of the "f" in the ligature glyph seems to be done by splitting it right down the middle, which doesn't actually fully colour the "f" red — part of the cross bar and the instroke are still black. OpenType contextual substitutions don't always render the entire context as a single glyph, like they do with ligatures. An example of that would be "calt" (contextual alternates) rendering "2x2" as "2×2", substituting x for a multiplication sign. With "frac" (fractions) you could have both: "1/2" could be rendered as a single glyph "½" or as a combination of superscript ¹, subscript ₂ and some form of slash, "¹/₂".

<rdar://problem/147874715>