<summary>
Line gap in font design units.
Recommended additional white space to add between lines to improve legibility. The recommended line spacing
(baseline-to-baseline distance) is thus the sum of ascent, descent, and lineGap. The line gap is usually
positive or zero but can be negative, in which case the recommended line spacing is less than the height
of the character alignment box.
</summary>
<summary> Line gap in font design units. Recommended additional white space to add between lines to improve legibility. The recommended line spacing (baseline-to-baseline distance) is thus the sum of ascent, descent, and lineGap. The line gap is usually positive or zero but can be negative, in which case the recommended line spacing is less than the height of the character alignment box. </summary>