- * the address of a variable containing the address of the first local
- * variable in the interpreter procedure
- * (this is used to find the frame where the pc is)
- * the address of the main interpreter loop
+ * the address of the program counter used in the interpreter procedure
+ * (px actually keeps the pc in a register if it can, but stores
+ * it in this location each time around the interpreter loop.)
+ * the address of the main interpreter loop (past the store of pc)