Category

<category> is an optional sub-element of <item>.

It has one optional attribute, domain, a string that identifies a categorization taxonomy.

The value of the element is a forward-slash-separated string that identifies a hierarchic location in the indicated taxonomy. Processors may establish conventions for the interpretation of categories. Two examples are provided below:

<category>Grateful Dead</category>
<category domain="http://www.fool.com/cusips">MSFT</category>

You may include as many category elements as you need to, for different domains, and to have an item cross-referenced in different parts of the same domain.