comment_email
comment_email is a filter on a commenter's e-mail address that is used in the comment_author_email_link() function. Note that it is a serious violation of your users' privacy to reveal their e-mail addresses using this function without their express permission. Make sure that you aren't using this function, or otherwise revealing e-mail addresses on public pages without express permission!
Context:
File: wp-includes/comment-functions.php
function comment_author_email_link($linktext='', $before='', $after='') {
global $comment;
$email = apply_filters('comment_email', $comment->comment_author_email);
if ((!empty($email)) && ($email != '@')) {
$display = ($linktext != '') ? $linktext : $email;
echo $before;
echo "<a href='mailto:$email'>$display</a>";
echo $after;
}
}
This hook is a filter which means that information is passed through it, and then used by WordPress. Your function needs to accept that information, and return it. Using add_filter('comment_email', 'your_function'); helps you to remember this distinction. When you are passing an ID, it is assumed that you will return the ID as it was given to you. With filters that pass strings or arrays, you may manipulate the information before passing it along.