The schema currently makes available within <facsimile> : surface,
surfaceGrp, and zone, but not line.
Is that balance about right? Should I restore <line> (which is sugar for
<zone type="line">) ? Should I remove <surfaceGrp>?
The purpose is to support a Simple document which contains just images
and the lightest of transcriptions, such as you might get from a crowd
sourcing transcription experiment for example, not to do full blown
genetic transcriptions, obvs.