alt - Based on the more peculiar glyph forms of the reference fonts
fantasy - Based on fonts used in fantasy games
halfloose - Halfloose width
halftight - Halftight width
large - Large height (16px)
loose - Loose width
mcr - Based on retrofuturistic MCR-like 8x8 fonts 
monospace - A monospaced typeface
sans - Sans-serif typeface
serif - Serif typeface
slab - Slab serif typeface
small - Small height (14px)
smallcaps - Small caps variant
tall - Double-height version
thin - Based on system fonts with 1-pixel-wide lines
tight - Tight width
ui - An UI typeface
xtralarge - Xtralarge height (17px)
xtrasmall - Xtrasmall height (13px)