Wash. Rev. Code § 35A.01.010
The purpose and policy of this title is to confer upon two optional classes of cities created hereby the broadest powers of local self-government consistent with the Constitution of this state. Any specific enumeration of municipal powers contained in this title or in any other general law shall not be construed in any way to limit the general description of power contained in this title, and any such specifically enumerated powers shall be construed as in addition and supplementary to the powers conferred in general terms by this title. All grants of municipal power to municipalities electing to be governed under the provisions of this title, whether the grant is in specific terms or in general terms, shall be liberally construed in favor of the municipality.
RCW 35A.01.010