Perhaps you just want to remove any patterns that are not allowed... 

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11152608
use warnings;

my @lines = split /^/, <<END;
xxx<pre>xxx<www>xxx<strong>xxx
xxx<pre>xxxxxx<strong>xxx
xxx<pre>xxx<pr>xxx<strong>xxx
xxx<pre>xxx<pree>xxx<strong>xxx
xxx<pre>xxx<strong>xxx<strong>xxx
xxx<pre>xxx<pre>xxx<strong>xxx
END

my %allowed = map { ( '<'.$_.'>' ) x 2 } qw( pre strong );
for ( @lines )
  {
  my $clean = s[<\w+>][ $allowed{$&} // '' ]ger;
  print $clean;
  }

[download]

Outputs: 

xxx<pre>xxxxxx<strong>xxx
xxx<pre>xxxxxx<strong>xxx
xxx<pre>xxxxxx<strong>xxx
xxx<pre>xxxxxx<strong>xxx
xxx<pre>xxx<strong>xxx<strong>xxx
xxx<pre>xxx<pre>xxx<strong>xxx

[download]

In reply to Re: perlre inverse check for several patterns by tybalt89
in thread perlre inverse check for several patterns by averlon

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