sinf — Scientific Inferiors
sinf (Scientific Inferiors) replaces lining or oldstyle figures with inferior figures sized for chemical and mathematical notation. It’s also used to replace lowercase letters with alphabetic inferiors.
Its difference from subs (Subscript) shows in how the Function field is written. subs’s Function says only “used to present subscript forms,” without naming which kind of glyph is affected or for what purpose. sinf’s Function narrows the target to figures and lowercase letters, and states the purpose explicitly as “primarily for chemical or mathematical notation.” The Recommended implementations differ too: subs is meant to combine a GSUB substitution with a GPOS position adjustment in two steps, while sinf is complete with the GSUB Single Substitution alone — the inferior glyph itself is already designed to sit below the standard baseline.
In real fonts, the two can point to the same glyphs regardless of this distinction. EB Garamond maps both subs and sinf to the same Unicode subscript digits (U+2080–2089), based on measuring EB Garamond’s GSUB table.
sups (Superscript) is its counterpart.
Example
Section titled “Example”.fea source
Writing it in a feature file
Section titled “Writing it in a feature file”The rules are written with Lookup Type 1.