Gallery Shortcode for REL tag?

You can do that, but it would require modifying the core (which I have been told is a no no).

No Core Mod:
Add this to your functions.php file in your theme:

add_filter('gallery_style', create_function('$a', 'return "
<div class=\'gallery\'>";'));

add_filter( 'wp_get_attachment_link' , 'add_lighbox_rel' );
function add_lighbox_rel( $attachment_link ) {
	if( strpos( $attachment_link , 'a href') != false && strpos( $attachment_link , 'img src') != false )
		$attachment_link = str_replace( 'a href' , 'a rel="lightbox" href' , $attachment_link );
	return $attachment_link;
}

and for good measure use the following jquery:

$(".gallery a, .lightbox, .gallery a[rel^='prettyPhoto'], a[rel^='prettyPhoto']").prettyPhoto({theme:'facebook'});

I use several different classes and attributes to cover all basis.

Core mod: go to your-wordpress-folder/wp-includes/post-template.php
Line 941 – Make it look like this:
return apply_filters( 'wp_get_attachment_link', "<a href='$url' rel='prettyPhoto[g]' title='$post_title'>$link_text</a>", $id, $size, $permalink, $icon, $text );

The [g] is to allow for the “gallery” function to activate.

Hope this helps!

Copy and paste the contents of your functions.php file here -> http://wordpress.pastebin.ca/
Then paste the link here.

This may be redundant, but I added the code to your pastie and pasted it here: http://pastie.org/855648 – Try that as your functions.php file.

If that doesn’t work, then you may be able to forget about adding the function all together and just use the jQuery to tell the standard gallery markup to lightbox. As I said, you would paste this into your header, just before </head>

<script src="text/javascript">
jQuery(document).ready(function($) {
$(".gallery a, .lightbox, .gallery a[rel^='prettyPhoto'], a[rel^='prettyPhoto']").prettyPhoto({theme:'facebook'});
});
</script>

Try that out and see what happens.

I use this in my themes. This automatically adds a rel="prettyPhoto" attribute within all <a> tags that link to an image. You can obviously change the attribute. The code is simple and self explanatory.

// Adapted and Modified from http://wordpress.org/extend/plugins/add-lightbox/
// Adds a rel="prettyPhoto" tag to all linked image files

add_filter('the_content', 'addlightboxrel_replace', 12);
add_filter('get_comment_text', 'addlightboxrel_replace');
function addlightboxrel_replace ($content)
{   global $post;
	$pattern = "/<a(.*?)href=('|\")([^>]*).(bmp|gif|jpeg|jpg|png)('|\")(.*?)>(.*?)<\/a>/i";
    $replacement = '<a$1href=$2$3.$4$5 rel="prettyPhoto['.$post->ID.']"$6>$7</a>';
    $content = preg_replace($pattern, $replacement, $content);
    return $content;
}

@amp343 That’s definitely a much simpler and more efficient solution. Thanks, I’ll give that a try as well.