Distance from the top extremum of the glyph to the bottom extremum.
Distance from the left extremum of the glyph to the right extremum.
Distance from the x-origin to the left extremum of the glyph.
Distance from the top extremum of the glyph to the y-origin.
Glyph extent values, measured in font units.
Note that @height is negative, in coordinate systems that grow up.