Does a new law apply prospectively or retroactively?

Concerning whether a new law applies both prospectively and retroactively, the rules are well established. No part of the Penal Code "is retroactive, unless expressly so declared." ( 3.) "[T]he language of section 3 erects a strong presumption of prospective operation, codifying the principle that, in the absence of an express retroactivity provision, a statute will not be applied retroactively unless it is very clear from extrinsic sources that the [lawmakers] ... must have intended a retroactive application. [Citations.] Accordingly, "a statute that is ambiguous with respect to retroactive application is construed ... to be unambiguously prospective." " ( People v. Brown (2012) 54 Cal.4th 314, 324, 142 Cal.Rptr.3d 824, 278 P.3d 1182.)