nsITransactionList in Firefox 1.5

 getChildListForItem() returns the list of children associated with the
 item at aIndex. Implementations may return null if there are no children,
 or an empty list. The list returned is AddRef'd so it is up to the caller
 to Release the transaction when it is done.
 @param aIndex The index of the item in the list.

 getItem() returns the transaction at the given index in the list. Note that
 a null can be returned here if the item is a batch. The transaction
 returned is AddRef'd so it is up to the caller to Release the transaction
 when it is done.
 @param aIndex The index of the item in the list.

 getNumChildrenForItem() returns the number of child (auto-aggreated)
 transactions the item at aIndex has.
 @param aIndex The index of the item in the list.

 itemIsBatch() returns true if the item at aIndex is a batch. Note that
 currently there is no requirement for a TransactionManager implementation
 to associate a toplevel nsITransaction with a batch so it is possible for
 itemIsBatch() to return true and getItem() to return null. However, you
 can still access the transactions contained in the batch with a call to
 getChildListForItem().
 @param aIndex The index of the item in the list.