COAH developed regulations under which the specific number of affordable units that each municipality would be required to provide (its "pre-credited need") could be determined. Participating municipalities developed compliance plans to address this need by such means as the application of credits ("e.g." filtering, spontaneous rehabilitation, extra credit for rental units), the use of regional contribution agreements (transferring part of the obligation to a willing municipality, usually an urban center, in the same region along with payment in an amount agreed by the municipalities) and zoning for affordable housing (usually involving increased density and mandatory set-asides). When COAH approved a municipality's compliance plan it would grant "substantive certification" which was designed to provide the municipality with protection from exclusionary zoning litigation.