Base Rate

Key _Base Rate in Infl Curve refers to the base rate.
It applies only when the Inflation Index is of type Relative
It is always set equal to the zero inflation swap rate associated with the first market instrument.
Look at Infl Curve for more information.

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.