diff --git a/blk.fs b/blk.fs
index e6ba921..18bf55a 100644
--- a/blk.fs
+++ b/blk.fs
@@ -2533,19 +2533,14 @@ sure it goes back to its previous level before next is called.
 
                                                         (cont.)
 ( ----- 441 )
-STABLE ABI: As a compatible binary, this binary follows the
-same stable ABI as its z80 counterpart.
+PS CHECKS: chkPS, is a bit different than in z80: it is para-
+metrizable. The idea is that we always call chkPS, before pop-
+ping, telling the expected size of stack. This allows for some
+interesting optimization. For example, in SWAP, no need to pop,
+chkPS, then push, we can chkPS and then proceed to optimized
+swapping in PS.
 
-PS CHECKS: Unlike z80 boot code, we don't check PS at each next
-call (we do check RS though). It is the responsibility of every
-native PSP-modifying word to call chkPS, . Also, chkPS, is a
-bit different than in z80: it is parametrizable. The idea is
-that we always call chkPS, before popping, telling the expected
-size of stack. This allows for some interesting optimization.
-For example, in SWAP, no need to pop, chkPS, then push, we can
-chkPS and then proceed to optimized swapping in PS.
-
-To assemble, load blocks 445 through 461
+Load range: B445-B461
 ( ----- 445 )
 VARIABLE lblexec VARIABLE lblnext
 H@ ORG !
diff --git a/doc/impl.txt b/doc/impl.txt
index a0a5b71..ac31e43 100644
--- a/doc/impl.txt
+++ b/doc/impl.txt
@@ -51,6 +51,10 @@ Stack underflow and overflow: In each native word involving
 PS popping, we check whether the stack is big enough. If it's
 not we go in "uflw" (underflow) error condition, then abort.
 
+This means that if you implement a native word that involves
+popping from PS, you are expected to call chkPS, for under-
+flow situations.
+
 We don't check RS for underflow because the cost of the check
 is significant and its usefulness is dubious: if RS isn't
 tightly in control, we're screwed anyways, and that, well