Deems a county inclusionary mandate as a form of development exaction and treats the mandate as a housing affordability impact fee. Provides parameters for a county's adoption or amendment of an inclusionary mandate for residential or mixed-use development. Establishes additional components for a needs assessment study for a county-imposed inclusionary mandate. Conditions the adoption or amendment of a county inclusionary mandate for residential or mixed-use development on written findings of essential nexus and rough proportionality and a determination of financial feasibility. (CD1)