Calculated position incorrect when using regex in text file that also contains binary info

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/CapHeight 667
>>
...
<<
/Length 422
>>

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my $result = $pdf=~qr/^1 0 obj/m;
say "Finding first item at start position  [$-[0]]" if $result;
...
 $result = $pdf=~qr/^4 0 obj/m;
say "Finding fourth item at start position [$-[0]]" if $result;
say "Finding fourth item at start position [$+[0]]\n" if $result;

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Finding first item at start position  [26]
Finding first item at start position  [33]
...

Finding fourth item at start position [2035]
Finding fourth item at start position [2042]

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