XXX.pm exports a function called XXX that you can put just about anywhere in
 your Perl code to make it die with a YAML dump of the arguments to its right.
 .
 The charm of XXX-debugging is that it is easy to type, rarely requires parens
 and stands out visually so that you remember to remove it.
 .
 XXX.pm also exports WWW, YYY and ZZZ which do similar debugging things.