You need to look at the '~literal' pseudo-element of HTML::Element.

If I understand your requirements correctly, the following code should do what you want. 

#!/usr/bin/perl
use warnings;
use strict;
my $html = <<'EOHTML';
<html>
 <body>
  <p>The relationship can be expressed by the following equation:<br>
  <blockquote>
    y &lt;= (7x<sup>3</sup> + 3x<sup>2</sup>)/((x - 3)(x - 5)
  </blockquote>

  <p>Of course x != 3 &amp; x != 5  --  That goes without saying.
 </body>
</html>
EOHTML

use HTML::TreeBuilder;

my $tree = HTML::TreeBuilder->new_from_content($html);

# Look for double-dashes in the text,
# and change them to &mdash;es.
$tree->look_down(sub {
  my $element = shift;
  my @content = $element->content_list();

  @content = map {
    if(ref) {
      $_       # Skip non-text children
    } else {

      # Break up the text child into pieces on the --'s
      my @texts = split /(--)/, $_;
      # Replaces those --'s with a ~literal
      # pseudo-element containing an &mdash;
      @texts = map {
        $_ eq '--'
          ? HTML::Element->new('~literal', text => '&mdash;')
          : $_
      } @texts;

      @texts;
    }
  } @content;

  # Replace the old content with the modified content
  $element->splice_content(0, scalar $element->content_list, @content)
+;

  return 0;
});

print $tree->as_HTML;

[download]

Update: The (formatted) output of the above is this: 

<html>
 <head>
 </head>
 <body>
  <p>The relationship can be expressed by the following equation:<br>
   <blockquote>
    y &lt;= (7x<sup>3</sup> + 3x<sup>2</sup>)/((x - 3)(x - 5)
   </blockquote>
  <p>Of course x != 3 &amp; x != 5 &mdash; That goes without saying.
 </body>
</html>

[download]

bbfu
Black flowers blossum
Fearless on my breath

In reply to Re: processing text nodes using HTML::Element by bbfu
in thread processing text nodes using HTML::Element by Anonymous Monk

Title:
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