+PERLVARI(I, tainted, bool, FALSE) /* using variables controlled by $< */
+
+/* PL_delaymagic is currently used for two purposes: to assure simultaneous
+ * updates in ($<,$>) = ..., and to assure atomic update in push/unshift
+ * @ISA, It works like this: a few places such as pp_push set the DM_DELAY
+ * flag; then various places such as av_store() skip mg_set(ary) if this
+ * flag is set, and various magic vtable methods set flags like
+ * DM_ARRAY_ISA if they've seen something of that ilk. Finally when
+ * control returns to pp_push or whatever, it sees if any of those flags
+ * have been set, and if so finally calls mg_set().
+ *
+ * NB: PL_delaymagic is automatically saved and restored by JUMPENV_PUSH
+ * / POP. This removes the need to do ENTER/SAVEI16(PL_delaymagic)/LEAVE
+ * in hot code like pp_push.
+ */