I understand some of the below but need explanation of what the undef and the mapping is doing?? I know it is saying dont use the fields in the qw part but not sure how it works?? 
use strict;
foreach my $field (param)
{
  #cover multivalued fields like checkboxes? Is this correct?
  foreach my $value (param($field))
  {
     #not sure what the mapping and undef are doing with the field var
+iable?
     next if exists
       { map {$_ => undef } qw(city state country) } -> { $field };
     #process non blank thedata variable
     if($value !~ /^\s*$/)
     {
         my $thedata .= "$field\:\t$value<br />";
         
     }
  }

}

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In reply to Explanation of mapping and undef by Anonymous Monk

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