MOF26 — as root Model element ?

The file http://www.omg.org/spec/MOF/20131001/MOF.xmi starts with:

<xmi:XMI xmlns:mofext="http://www.omg.org/spec/MOF/20131001" xmlns:uml="http://www.omg.org/spec/UML/20131001" xmlns:xmi="http://www.omg.org/spec/XMI/20131001">
<packagedElement xmi:type="uml:Package" xmi:id="_MOF" name="MOF">
...

Is it correct to have <packagedElement> as root Model element ?

Why isn't it :

<xmi:XMI xmlns:mofext="http://www.omg.org/spec/MOF/20131001" xmlns:uml="http://www.omg.org/spec/UML/20131001" xmlns:xmi="http://www.omg.org/spec/XMI/20131001">
<uml:Package xmi:id="_MOF" name="MOF">
...

Thanks