The Licenses Section

Each document may contain one optional license element. The absence of this element means that there is no license and that no permissions should be assumed by anyone but the owner(s).

<license>
    <url>https://burritos-r-us.org/licenses/3247</url>
</license>

<!-- or -->

<license>
    <publicDomain/>
</license>

publicDomain

This empty element indicates that the document is in the public domain (and thus that no license is provided or needed in order to use the burrito.)

url

This element contains a link to the license. (In the case of private licenses the link may not be accessible to all users, but it still acts as a stable identifier).