The 'usual' way of achieving this is to use the flip flop operator (or range operator). 
use warnings;
use strict;

use autodie;

while (<DATA>) {
    next if (/<!--/ .. /-->/);
    print;
}

__DATA__
<html>
    <head>
    <!--
    some 
    html
    comment
    -->
    </head>
    <body>
    <!--
    some 
    multi-line
    html
    comment
    -->
    </body>
</html>

[download]
Giving 
$ perl tst.pl
<html>
    <head>
    </head>
    <body>
    </body>
</html>

[download]
A user level that continues to overstate my experience :-))

In reply to Re: Remove multiple lines between two patterns by Bloodnok
in thread Remove multiple lines between two patterns by jcvivar

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