Source
File: wp-admin/includes/meta-boxes.php
function post_trackback_meta_box( $post ) {
$form_trackback = '<input type="text" name="trackback_url" id="trackback_url" class="code" value="' .
esc_attr( str_replace( "\n", ' ', $post->to_ping ) ) . '" aria-describedby="trackback-url-desc" />';
if ( '' !== $post->pinged ) {
$pings = '<p>' . __( 'Already pinged:' ) . '</p><ul>';
$already_pinged = explode( "\n", trim( $post->pinged ) );
foreach ( $already_pinged as $pinged_url ) {
$pings .= "\n\t<li>" . esc_html( $pinged_url ) . '</li>';
}
$pings .= '</ul>';
}
?>
<p>
<label for="trackback_url"><?php _e( 'Send trackbacks to:' ); ?></label>
<?php echo $form_trackback; ?>
</p>
<p id="trackback-url-desc" class="howto"><?php _e( 'Separate multiple URLs with spaces' ); ?></p>
<p>
<?php
printf(
/* translators: %s: Documentation URL. */
__( 'Trackbacks are a way to notify legacy blog systems that you’ve linked to them. If you link other WordPress sites, they’ll be notified automatically using <a href="%s">pingbacks</a>, no other action necessary.' ),
__( 'https://wordpress.org/support/article/introduction-to-blogging/#comments' )
);
?>
</p>
<?php
if ( ! empty( $pings ) ) {
echo $pings;
}
}