# Note-form on ISAMUX (aka "ISANS")
+Links:
+
+* <http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2020-February/004190.html>
+
A fixed number of additional (hidden) bits, conceptually a "namespace", that go directly and non-optionally
into the instruction decode phase, extending (in each implementation) the
opcode length to 16+N, 32+N, 48+N, where N is a hard fixed quantity on