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: Codex URL */
		__( 'Trackbacks are a way to notify legacy blog systems that you&#8217;ve linked to them. If you link other WordPress sites, they&#8217;ll be notified automatically using <a href="%s">pingbacks</a>, no other action necessary.' ),
		__( 'https://codex.wordpress.org/Introduction_to_Blogging#Managing_Comments' )
	);
	?>
</p>
	<?php
	if ( ! empty( $pings ) ) {
		echo $pings;
	}
}