bah, can't fork/update the anonymous gist anymore, so here is a patch to explain /(?^:foo$)/m is the same as /(?-xism:foo$)/m
--- ppixregexplain.pl 2014-02-04 23:58:11.265625000 -0800
+++ ppixregexplain-dodgy-bug.pl 2014-12-30 20:54:31.250000000 -0800
@@ -1159,6 +1159,10 @@
#~ delete @mods{@offers} ; ## OFFERS TRUMP ONNERS
$mods{$_}=0 for @offers ; ## OFFERS TRUMP ONNERS
+ if( $con eq '^' ){
+ $mods{$_}=0 for qw/ i m s x /; ## d-imsx http://perldoc.
+perl.org/perlre.html#%28?^alupimsx%29
+ }
+
@mods = ( @onners, @offers );
if( $notroot ){