Which Magento Domain Objects Use Layout XML Updates?

Question

Is there a canonical list (public or private-that-you're-willing-to-share) of Magento objects (and their database persistance tables) that allow you add Layout XML Updates to the system? I realize there's an almost infinite number with third party modules, but I'm specifically interested in what ships with CE, Professional, and Enterprise Edition.

In case that's not clear, consider Magento's CMS pages. In the CMS admin there's a textarea for

Layout Update XML

in the Design tab.

This XML is persisted to the database with the CMS Page object, and these updates are added to the Layout object when that page is loaded.

There's multiple places in the Magento admin where this happens. I'm looking for a list of all of them.

Answer 1

I had trouble filtering by a specific branch with Google's search operators, but this is a decent start: https://www.google.com/search?q=%22custom_layout_update%22+site%3Asvn.magentocommerce.com

Answer 2

Not many that I can see,

Mage/Catalog/Model/Category.php
Mage/GoogleBase/Model/Attribute.php

And the CMS module as mentioned above.