(PHP 5 >= 5.0.1)
tidyNode::isComment — Checks if a node represents a comment
Tells if the node is a comment.
   Returns TRUE if the node is a comment, FALSE otherwise.
  
Example #1 Extract comments from a mixed HTML document
<?php
$html = <<< HTML
<html><head>
<?php echo '<title>title</title>'; ?>
<# 
  /* JSTE code */
  alert('Hello World'); 
#>
</head>
<body>
<?php
  // PHP code
  echo 'hello world!';
?>
<%
  /* ASP code */
  response.write("Hello World!")
%>
<!-- Comments -->
Hello World
</body></html>
Outside HTML
HTML;
$tidy = tidy_parse_string($html);
$num = 0;
get_nodes($tidy->html());
function get_nodes($node) {
    // check if the current node is of requested type
    if($node->isComment()) {
        echo "\n\n# comment node #" . ++$GLOBALS['num'] . "\n";
        echo $node->value;
    }
    // check if the current node has childrens
    if($node->hasChildren()) {
        foreach($node->child as $child) {
            get_nodes($child);
        }
    }
}
?>
The above example will output:
# jste node #1
<# 
  /* JSTE code */
  alert('Hello World'); 
#>
Note:
This function was named tidy_node::is_comment() in PHP 4/Tidy 1.