I don't know about a completely general HTML solution because I am not an HTML expert. However, it could be that something simple would work ok? Here is some code that stops printing <nav sections after it has seen the first one. You could adapt this to your desired nth parameter functionality. 
use strict;
use warnings;

my $nav_seen =0;

while (<DATA>) 
{
   # if inside of <nav> section, print it
   # unless we have seen a <nav> section before
   
   if (my $status = /<nav/ ... /<\/nav/) 
   { 
      print unless $nav_seen;
      $nav_seen++ if $status =~ /E/;
   }
   else {print}    
}
=PRINTOUT
<body>   

<nav a=b>   

 <div>   
 </div>   
</nav>   
  
<div>   
</div>   


</body> 

=cut

__DATA__
<body>   

<nav a=b>   

 <div>   
 </div>   
</nav>   
  
<div>   
</div>   

<nav c=d>    
  <li> </li>      
</nav>   

</body>

[download]
To understand how this works, I direct you to Flipin good, or a total flop?.

In reply to Re: How do we remove specific HTML tag by Marshall
in thread How do we remove specific HTML element by abdan

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