rdf parse-able

Where do I find information on the requirements for writing XML so that
it is RDF parse-able.  I believe some people might refer to this as
embedded RDF.
 
I have read through the RDF/XML Syntax Specification and section 2.6
states that the RDF-XML must be enclosed in an rdf:RDF tag.
 
However, the rdf validator page (http://www.w3.org/RDF/Validator/) has a
check box to specify that the XML entered does not have the RDF tag.
 
So I think my question is, when you check that checkbox and you paste in
some XML what are the rules you need to follow in order for that XML to
be validated as RDF parse-able?
What spec are these rules in or where can I find them?
 
I am trying to make sure that an XML schema we are creating is RDF parse
able because an instance of that schema will end up as instances in our
RDF/RDF ontology.
 
Thanks