Sorting by Custom Item Type Attributes?

I’m currently working on a database that required a new item type for some specific fields not well handled in Dublin Core. What I would like to do is be able to add specific attributes as a sort option in the browse items (that browse.php file seems to control it). Specifically, I have model nos. for pieces of furniture and I would like to use that as a sorting option on the browse page.

Clearly I am missing something here, but it seems as though it should be possible. Putting in the item type here doesn’t work for me:

<?php $sortLinks[__('Title')] = 'Dublin Core,Title'; $sortLinks[__('Creator')] = 'Dublin Core,Creator'; $sortLinks[__('Date Added')] = 'added'; ?>

How do I point this $sortlinks command to the information I need it to gather?

Any help is much appreciated.

The element set for all item type elements is Item Type Metadata, so you should be able to sort by it using the string Item Type Metadata,YourElement where YourElement is the name of the custom element you want to sort by.