Tip #9 from the Basic debugging checklist : YAPE::Regex::Explain

The regular expression:

(?-imsx:(ther*))

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    the                      'the'
----------------------------------------------------------------------
    r*                       'r' (0 or more times (matching the most
                             amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
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Use . instead. Also, with different delimiters, you can clean up the replacement string:

use warnings;
use strict;

my $test = "Here is the there";
$test =~ s{(ther.)}{<test>$1</test>}ig;
print "$test\n";

__END__

Here is the <test>there</test>
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