notes on redo semantics, restrict to lexotic

S04-control.pod

@@ -12,8 +12,8 @@ Synopsis 4: Blocks and Statements
 
     Created: 19 Aug 2004
 
-    Last Modified: 4 Nov 2013
-    Version: 128
+    Last Modified: 12 Nov 2013
+    Version: 129
 
 This document summarizes Apocalypse 4, which covers the block and
 statement syntax of Perl.
@@ -80,6 +80,16 @@ discover that identity), but for the dynamic fallback, the exception
 will contain only the loop label to be matched dynamically.  See
 L</Control Exceptions> below.
 
+The C<redo> operator, as a variant of C<goto>, directly transfers
+control to the first statement of the lexotically enclosed loop.
+Essentially, the compiler turns it into a C<goto> with an implicitly
+generated (secret) label on that first statement.  In order to know
+when that implicit label must be generated, we restrict C<redo> to
+the current outer lexical scope.  It may not be used dynamically.
+(If you find yourself wanting the dynamic variant, please use C<goto>
+with an explicit label instead, so the compiler can know to pessimize
+any unrolling of that loop.)
+
 =head1 The Relationship of Blocks and Declarations
 
 Every block is a closure.  (That is, in the abstract, they're all