more clarifications and notes

uxntal.1

@@ -64,7 +64,11 @@ For example the generic effect for \fBADD\fP is ( x y -- x+y ). The eight combin
     \fBADD2k\fP  ( x* y*   -- x* y* x+y* )   sum two shorts using \fBwst\fP, retain arguments
     \fBADD2kr\fP ( [x* y*] -- [x* y* x+y*] ) sum two shorts using \fBrst\fP, retain arguments
 
-Thus for regular instructions writing a "generic" effect (leaving sigils off values whose size depends on \fIshort\fP mode) is sufficient to describe its behavior across all eight variations. Note that some instructions always read values of a fixed size. (For example the boolean condition read by \fBJCN\fP is always one byte, no matter what modes are used.)
+Thus for regular instructions writing a "generic" effect (leaving sigils off values whose size depends on \fIshort\fP mode) is sufficient to describe its behavior across all eight variations. Note that some instructions always read values of a fixed size. For example the boolean condition read by \fBJCN\fP is always one byte, no matter what modes are used.
+
+In \fIreturn\fP mode the stacks are reversed. Effects on \fBwst\fP will instead affect \fBrst\fP, and effects on \fBrst\fP will instead affect \fBwst\fP. For example, \fBSTH\fP reads a byte from \fBwst\fP and writes it to \fBrst\fP, but \fBSTHr\fP reads a byte from \fBrst\fP and writes it to \fBwst\fP.
+
+In \fIkeep\fP mode all the values on the left-hand side of the stack effect will also appear on the right-hand side before the outputs. For example, \fBSWP\fP is \fB(x y -- y x)\fP but \fBSWPk\fP is \fB(x y -- x y y x)\fP.
 
 .SS INC
 ( x -- x+1 )
@@ -72,6 +76,8 @@ Thus for regular instructions writing a "generic" effect (leaving sigils off val
 .SS POP
 ( x -- )
 
+\fBPOPk\fP is guaranteed to have no effect (it will not change the stack).
+
 .SS NIP
 ( x y -- y )