Colons in Prefix Names?

I got confused by the examples given in the PR OWL 2 Primer at

<http://www.w3.org/TR/2009/PR-owl2-primer-20090922/>

regarding the exact syntax for prefix names.

According to the PR OWL 2 Structural Specification at

<http://www.w3.org/TR/2009/PR-owl2-syntax-20090922/#IRIs>

the last character should always be a colon (see also the PNAME_NS  
production in <http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/ 
 >). This is also the case for all examples given in Functional Style  
Syntax, e.g. those in
<http://www.w3.org/TR/2009/PR-owl2-primer-20090922/#Appendix:_The_Complete_Sample_Ontology 
 >

Prefix(:=<http://example.com/owl/families/>)
Prefix(otherOnt:=<http://example.org/otherOntologies/families/>)
Prefix(xsd:=<http://www.w3.org/2001/XMLSchema#>)
Prefix(owl:=<http://www.w3.org/2002/07/owl#>)
..

However, the corresponding example in OWL/XML Syntax has the following  
entry

   <Prefix name="otherOnt" IRI="http://example.org/otherOntologies/families/ 
"/>

which complies with the OWL 2 XML Schema. Note that here the name of  
the prefix does not contain a colon. I would have expected the  
following:

   <Prefix name="otherOnt:" IRI="http://example.org/otherOntologies/families/ 
"/>

What is the correct way to specify a prefix in OWL/XML Syntax? Would  
the empty prefix be defined with name="" or name=":"?

Best regards,
Marko Luther