QL Observation Lag

Key _QL Observation Lag in Infl Curve refers to the observation lag as conveyed directly from QuantLib.
Expects an object of type Step.

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.