2011-02-23   Rocket Fuel
    Expense:Travel   $100000000.00 ; trip: Moon 
    Asset:NASA

2011-02-23   Liquid Oxygen
    Expense:Travel  $232233223.00  ; trip: Moon
    Asset:NASA

test bal --group-by "tag('trip')"
Moon
       $332233223.00  Expense:Travel
end test
