#... at the start of your code ...
     # notice how exception definition and message format
     # string constant are in two different places and need
     # to be manually coordinated by the programmer.

     use Exception::Class {
       'Exception::Copy::Mine' {
           fields => [qw(from to)];
        }
        # ... lots of other exceptions here ...
     }
     my $MSG_COPY='Could not copy A.txt to B.txt";

     ... later on when you throw the exception ...

     # notice the repetition in the use of exception
     # properties; the repetition is error prone and adds
     # unnecessary extra typing     

     my $sMsg = sprintf($MSG_COPY, 'A.txt', 'B.txt');
     Exception::Copy::Mine->throw(error => $sMsg
                                  , from => 'A.txt'
                                  , to => 'B.txt');