create RDF namespace from a script? fourth parameter of Assert? xul-rule for existance of a property?

Some questions:

1. A manually written file in firefox can declare MYNS as namespace, but
when creating from script it's labeled NS1,NS2 ... etc.

Is there a way of forcing the use of MYNS?

<?xml version="1.0"?>
<RDF:RDF xmlns:MYNS="http://www.somepage-of-somewhere.com/path#"
         xmlns:NC="http://home.netscape.com/NC-rdf#"
         xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
...

I think it's possible somehow to manually use xml/rdf writer, but I'm only 
interested in combination with the normal rdf service, because I wan't to 
have the datasources sync.

2. Can someone explain the fourth parameter of Assert (the truthvalue)?

xulplanet say's only rarely used.

3. Is there a way to display elements in a xul-template dependend on the 
existance of a value?

I have a rdffile like this one:

<?xml version="1.0"?>
<RDF:RDF xmlns:XX="http://www.somepage-of-somewhere.com/path#"
         xmlns:NC="http://home.netscape.com/NC-rdf#"
         xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <RDF:Description 
RDF:about="http://www.somepage-of-somewhere.com/somepage/xx"
                   XX:blocked="false" />
  <RDF:Description 
RDF:about="http://www.somepage-of-somewhere.com/somepage/yy"
                   XX:blocked="false" />
  <RDF:Description 
RDF:about="http://www.somepage-of-somewhere.com/somepage/licensed"
                   XX:license="admin" />
  <RDF:Seq RDF:about="http://www.somepage-of-somewhere.com/root#">
    <RDF:li 
RDF:resource="http://www.somepage-of-somewhere.com/somepage/xx"/>
    <RDF:li 
RDF:resource="http://www.somepage-of-somewhere.com/somepage/yy"/>
    <RDF:li 
RDF:resource="http://www.somepage-of-somewhere.com/somepage/licensed"/>
  </RDF:Seq>
</RDF:RDF>

And wan't to display all items that have the blocked property.

In this case I simply could add <rule XX:blocked=true ...  and <rule 
XX:blocked=false ...
but if blocked is a string thats not possible  and <rule XX:license=RDF:*> 
doesn't work
I tried getting into advanced rules .. without success.

Thx
  Harry