Links:
* <http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2020-February/004190.html>
+* bugreport <http://bugs.libre-riscv.org/show_bug.cgi?id=214>
A fixed number of additional (hidden) bits, conceptually a "namespace",
set by way of a CSR or other out-of-band mechanism,