Attribution
An attribution must specify its type, and an amount. Any of the three amount fields
below can be used (and they can all be used at the same time), as long as they are
used consistently. You can express an attribution in a maximum of three different
currencies (settlement, base, underlying), which are usually the same as the settlement
currency on the trade, the base currency used for accounting purposes, and the underlying
currency which refers to the currency of an underlying instrument used in a transaction.
Note however that these are just guidelines; you can actually specify attributions
in any currency that you like, as long as you are consistent. Within an Attributions
structure, all attribution/settlementAmounts are expressed in the same currency, defined
by the settlementCurrency field (see enclosing Attributions structure). Same holds
true for base and underlying amounts.