What is the difference between properties and attributes in HTML

Question

I've been trying to define the difference between properties and attributes in HTML since the changes in jQuery 1.6.1.

According to the list on the jQuery 1.6.1 release notes (near the bottom), HTML properties and attributes can be classified as follows:

Properties: Any property that has a boolean value or is calculated by UA, such as selectedIndex.

Attributes: 'Attributes' that can be added to an HTML element that is neither boolean nor contains a value generated by the user agent.

Thoughts?