All fonts have a natural baseline defined by the position of each glyph in the font's em-square.
Quickdraw GX fonts may include additional information which identifies other baseline positions to which glyphs may be aligned. There are 32 pre-defined baseline values. Baselines with values of 0 through 4 should be provided for all horizontal Quickdraw GX fonts. The baseline appears near the bottom of the entire line. 1 Ideographic centered baseline.