How to create a scripted weight

A scripted weight contains one weight set definition. 

Example

<wset id="GenRegAge" pop="3547" decimals="0">
      <text>Population</text>
      <rim>
         <rimcell expr="\1.A=1&\2.A=1&\3.A=1" pop="148" />
         <rimcell expr="\1.A=1&\2.A=1&\3.A=2" pop="282" />
         <rimcell expr="\1.A=1&\2.A=2&\3.A=1" pop="73" />
         <rimcell expr="\1.A=1&\2.A=2&\3.A=2" pop="120" />
         <rimcell expr="\1.A=1&\2.A=3&\3.A=1" pop="38" />
         <rimcell expr="\1.A=1&\2.A=3&\3.A=2" pop="65" />
         <rimcell expr="\1.A=1&\2.A=4&\3.A=1" pop="26" />
         <rimcell expr="\1.A=1&\2.A=4&\3.A=2" pop="45" />
         <rimcell expr="\1.A=2&\2.A=1&\3.A=1" pop="144" />
         <rimcell expr="\1.A=2&\2.A=1&\3.A=2" pop="275" />
         <rimcell expr="\1.A=2&\2.A=2&\3.A=1" pop="69" />
         <rimcell expr="\1.A=2&\2.A=2&\3.A=2" pop="113" />
         <rimcell expr="\1.A=2&\2.A=3&\3.A=1" pop="37" />
         <rimcell expr="\1.A=2&\2.A=3&\3.A=2" pop="60" />
         <rimcell expr="\1.A=2&\2.A=4&\3.A=1" pop="24" />
         <rimcell expr="\1.A=2&\2.A=4&\3.A=2" pop="42" />
      </rim>
   </wset>