I was able to get XML::Simple to read in that data just fine. However, I did notice that your opening "declaration" tag was missing the ">" at the end of that line. Not sure if that is missing in your original data or if this was a just a "cut & paste" mistake in your post.

Here's the contents of sample.xml:

<declaration dd:maxOccur="-1" dd:minOccur="0" dd:nullType="exclude"> 
  <contentDeclaration dd:minOccur="0" dd:nullType="exclude"/>
  <value dd:minOccur="0" dd:nullType="exclude"/>
</declaration>
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Here's the code I ran:

use strict;
use warnings;

use XML::Simple;
use Data::Dumper;

my $xml = XMLin('sample.xml');

print Dumper($xml);
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And here's the output:

$VAR1 = {
          'dd:minOccur' => '0',
          'contentDeclaration' => {
                                  'dd:minOccur' => '0',
                                  'dd:nullType' => 'exclude'
                                },
          'value' => {
                     'dd:minOccur' => '0',
                     'dd:nullType' => 'exclude'
                   },
          'dd:maxOccur' => '-1',
          'dd:nullType' => 'exclude'
        };
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