Impl Vol Spec

Key Impl Vol Spec in Vol Curve refers to an optional object of type Impl Vol Spec that is used only if Sparse Conv Mkt Vols? = true or Sparse Impl Vols? = true, in which case it serves to define the type of vols displayed in _Sparse Conv Mkt Vols and _Sparse Impl Vols respectively.
Most importantly, this entry defines the Vol Type of the produced implied vols, which may differ from the entry for the key Vol Type embedded in the Vol Ref object assigned to the key Vol Ref