how to validate a non empty element with only attributes

[edkawas]

Hi,

I have a schema that validates the following:

<foo:GFF xmlns:foo="http://www.foo.org/foo" foo:articleName=""
foo:id="" foo:namespace=""/>

What should i do so that only the following is valid:
<foo:GFF xmlns:foo="http://www.foo.org/foo" foo:articleName=""
foo:id="" foo:namespace="">blah blah blah</foo:GFF>

Thanks,

Ed