Clarify junctional short-circuiting

Closes #2120

doc/Type/Junction.pod6

@@ -56,9 +56,12 @@ C<Junction> come into play:
     say    %h{one <foo  bar>}:exists; # OUTPUT: «one(True, True)␤»
     say so %h{one <foo  bar>}:exists; # OUTPUT: «False␤»
 
-Note that the compiler is allowed to parallelize and short-circuit
-autothreading (and Junction behavior in general), so it is usually an error
-to autothread junctions over code with side effects.
+Note that the compiler is allowed, but not required, to parallelize
+and, where possible, short-circuit autothreading (and Junction behavior
+in general), so it is usually an error to autothread junctions over code
+with side effects. When short-circuiting is involved (e.g. when evaluating
+a L<Junction> in boolean context), its order is not guaranteed and is done
+for performance purposes only.
 
 Junctions are meant to be used as matchers in boolean context; introspection
 of junctions is not supported. If you feel the urge to introspect a junction,