An icon-specific field containing the data from the icon mask.
<p>
This is a 1 bit bitmap stored with the most significant
bit first. The number of bytes per scanline is
'((width + 7) / 8 + (maskPad - 1)) / maskPad * maskPad'.
</p><p>
The default is null which means 'no transparency mask'.
</p>
An icon-specific field containing the data from the icon mask. <p> This is a 1 bit bitmap stored with the most significant bit first. The number of bytes per scanline is '((width + 7) / 8 + (maskPad - 1)) / maskPad * maskPad'. </p><p> The default is null which means 'no transparency mask'. </p>