liarandathief

Try this function from the the Conditional Tags Page:

function is_tree($pid) {      // $pid = The ID of the page we're looking for pages underneath
	global $post;         // load details about this page
	$anc = get_post_ancestors( $post->ID );
	foreach($anc as $ancestor) {
		if(is_page() && $ancestor == $pid) {
			return true;
		}
	}
	if(is_page()&&(is_page($pid)))
               return true;   // we're at the page or at a sub page
	else
               return false;  // we're elsewhere
};

it recognizes any ancestor child, grandchild, etc. Add this to your functions.php and call with is_tree(‘id’)

I needed something similar for outputting the page list in a custom xml document, so I could read it with another program.

I used wp_list_pages() with a slight modification to two files: post-template.php and classes.php

first post-template.php (this is where the wp_list_pages function sits):
In the function, add a custom argument
'wrapper_tag' => 'li'
to the $defaults array. That’s it for that file. Then in classes.php, find the Walker_Page Class and find the line that reads:
$output .= $indent . '<li class="' . $css_class
and change it to:
$output .= $indent . "<$wrapper_tag class=\"" . $css_class
then, a little further on, change:

function end_el(&$output, $page, $depth) {
        $output .= "</li>\n";
    }

to:

function end_el(&$output, $page, $depth,$args) {
        extract($args, EXTR_SKIP);
        $output .= "</$wrapper_tag>\n";
    }

You see I included all the $args and extracted them just to get the $wrapper_tag, so this may not be the most efficient solution, but it works. I probably should have created my own funtion/class, but I’m lazy.

Finally, to use it, just use:
wp_list_pages('title_li=&depth=1&wrapper_tag=whatever');