XML Schema: What does <include schemaLocation="" /> mean?

Hi Folks,

Today, by accident, I omitted the value of schemaLocation in an xs:include, i.e.,

    <xs:include schemaLocation="" />

The Oxygen tool put a red squiggly line under it, to alert me. When I hovered my mouse over it, I got this (Saxon) warning message: 

    MySchema.xsd recursively includes itself

Interesting!

Given that the message was a warning and not an error, I conclude that it is legal for a schema file to include itself. Neat! Is there a use case for doing so? 

/Roger