+ * Registers in the STG machine.
+ *
+ * The STG machine has a collection of "registers", each one of which
+ * may or may not correspond to an actual machine register when
+ * running code.
+ *
+ * The register set is backed by a table in memory (struct
+ * StgRegTable). If a particular STG register is not mapped to a
+ * machine register, then the apprpriate slot in this table is used
+ * instead.
+ *
+ * This table is itself pointed to by another register, BaseReg. If
+ * BaseReg is not in a machine register, then the register table is
+ * used from an absolute location (MainCapability).