How to represent bits with a required zero value? #31

Pixel formats have padding when channel bit ranges don't cover all bits (e.g. 10-bit formats with 3 channels may have 2 bits of padding). For some formats the padding may contain arbitrary/undefined contents, but for some others the padding must be filled with zeroes. Examples include DRM_FORMAT_Y210 and AV_PIX_FMT_P010.

How would one represent such bits with KDFS?

KDFS defines constant virtual bits, but I haven't found a way to use these to represent such required zero values.