updated 5/7/2020

Reads are made by direct calls (not buffered), but if dynamic values are being read
and an actual write is taking place the reads are temporarily blocked.

If bit 2 of 'type' is set on entry then the command is passed on to the limits tests
- see Limits.txt

In general it returns a float representing the wanted element.

If bit 7 of 'type' is returned as set this should be regarded as an integer.

If bit 5 is returned as set then the control is MIDI-learnable.