User Guide

Making OpenType Fonts
673
Glyph Geometry
Positioning lookups may change one of the glyph positioning metrics:
Placement X and Y Advance X and Y
A single positioning lookup may tweak any of four values: placement_X,
placement_Y, advance_Y and advance_Y.
Modification of the origin point of the glyph will shift it and all following
glyphs. Modification of the advance vector will shift the next glyph in the
glyph string.