lMaxBaselineExt (LONG)
The maximum vertical space occupied by the font, in world coordinate units. This is the sum of lMaxAscender and lMaxDescender if both are positive. It is also the sum of lInternalLeading and lEmHeight.
One possible type of line spacing can be computed by adding lMaxBaselineExt to lExternalLeading. Such a line spacing, however, would be dependent on the glyph set included in the font. If a new version of the font should be made available, with new glyphs, then it is possible that this value will change because one of the new glyphs has gone above the previous lMaxAscender or below the previous lMaxDescender. More sophisticated applications will base line spacing on the point size (lEmHeight) of the font, which is an invariant of the font, multiplied by some factor (for example, 120%) plus any external leading.
This field may exceed lEmHeight.