Devel::Peek contains functions which allows raw Perl
       datatypes to be manipulated from a Perl script.  This is
       used by those who do XS programming to check that the data
       they are sending from C to Perl looks as they think it
       should look.  The trick, then, is to know what the raw
       datatype is supposed to look like when it gets to Perl.
       This document offers some tips and hints to describe good
       and bad raw data.

       Devel::Peek supplies a Dump() function which can dump a
       raw Perl datatype, and mstat("marker") function to report
       on memory usage (if perl is compiled with corresponding
       option).  The function DeadCode() provides statistics on
       the data "frozen" into inactive CV.  Devel::Peek also
       supplies SvREFCNT(), SvREFCNT_inc(), and SvREFCNT_dec()
       which can query, increment, and decrement reference counts
       on SVs.