<summary>
Horizontal size of the subscript em box in design units, used to
scale the simulated subscript relative to the full em box size.
This the numerator of the scaling ratio where denominator is the
design units per em. If this member is zero, the font does not specify
a scale factor, and the client should use its own policy.
</summary>
<summary> Horizontal size of the subscript em box in design units, used to scale the simulated subscript relative to the full em box size. This the numerator of the scaling ratio where denominator is the design units per em. If this member is zero, the font does not specify a scale factor, and the client should use its own policy. </summary>