difficulty understanding elementFormDefault attribute

Hi,

there is an aspect of the elementFormDefault attribute that I don't
understand.
I read that  the value 'qualified' for elementFormDefault is  a directive to
instance documents for the elements declared in the schema to be namespace
qualified.
However, I have seen valid schemas that contain
elementFormDefault="qualified" but have no target namespace defined(do not
contain the attribute targetNamespace)

If no target namespace is defined, how can the elements that conform to the
given schema in an instance document be namespace qualified?

Thanks a lot.