Problem with PHP shorthand

I have a jQuery image rotating script that I found, which uses a line like this to call the images that get rotated:

<?=$image_rotation; ?>

When I save this as a snippet, MODx rewrites it thusly:

<?php
=$image_rotation;
?>

And then I get this lovely error on the page with the script on it:
Parse error: syntax error, unexpected ’=’ in /home/jademoun/public_html/manager/includes/document.parser.class.inc.php(769) : eval()’d code on line 1

I understand why I get the error, but I can’t figure out how to resolve it. I understand that <?= is shorthand for something in PHP, but I’m not sure what, and that’s a hard thing to Google for. Any help would be appreciated!

Try it with this as your snippet code:

<?php
$output ="";
$output .=$image_rotation;
return $output;
?>

That’s shorthand for echo. You shouldn’t use echo in snippets, all output should be gathered into a variable and returned.