FacetDocs

Font

font   = [family] size ["/" line] [word ...]
family = every word before the first number or keyword ("Instrument Sans")
size   = number, in pixels
line   = number of pixels | number "%" | multiple of the size, up to 4 ("1.4")
word   = weight | "italic" | spacing | case
weight = 100 … 900 in hundreds | thin | extralight | light | regular | medium | semibold | bold | extrabold | black
spacing= "+" or "-" then pixels ("+0.4") or a percentage ("-2%")
case   = caps | upper | lower | title
FontfontFamilyfontSizelineHeightfontWeightother
Inter 15/22Inter1522
Fraunces 44/1.1 600 -1Fraunces44110%600letterSpacing −1
12/16 700 +1.6 capsinherited1216700letterSpacing 1.6, upper case
Tiro Devanagari Hindi 20/28Tiro Devanagari Hindi2028

The first number is always the size, so write a weight after it. A family from Google Fonts is downloaded the first time a build names it.