I need to retract my earlier statement 
Listing several techs does not necessarily make it "OR"
For example, consider the Kingdom tech Light Armor that requires TWO techs before it becomes available.
<Prereq>
<Type>Tech</Type>
<Attribute>Cutting_Weapons_Amarian</Attribute>
<Value>0</Value>
</Prereq>
<Prereq>
<Type>Tech</Type>
<Attribute>Blunt_Weapons_Amarian</Attribute>
<Value>0</Value>
</Prereq>
I believe that the <value> tags give additional meaning to the prereq, although I haven't tested that.
Anyway that is good news because it means our tech trees don't just branch off but can combine as well.