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# html
# Note that if the user selects the checkbox, the value is 'on'
...
  print Dumper(%hash);
  exit(0);
}

# Dumped
$VAR1 = 'Place'; $VAR2 = undef; $VAR3 = 'data'; $VAR4 = 'field';

# Dumped
$VAR1 = 'data'; $VAR2 = 'on'; $VAR3 = 'field'; $VAR4 = 'Place';