Notional

Key _Notional in BondExt refers to the 1D-array of notionals that apply on the successive coupon periods.
It consists of N+1 elements, where N is the number of bond accrual periods.
The first element is the notional applying at the begining of the first accrual period and determines the initial paid amount in a context where such an initial payment is prescribed.
The last element is the notional applying at the maturity of the bond and determines the terminal paid amount after it is multiplied with the bond's Redemption

Note this key is prefixed by _, which indicates it is regarded as a read-only part of the object's data and therefore its associated value cannot be edited.
For that reason it does not appear as part of the input data.
It carries informational only value for the user and appears as part of its contents.
Also it completely depends on the remaining object contents and therefore is never part of the exported object's data.