Wash. Rev. Code § 35A.21.020
This optional municipal code is intended to be a general law, available to all cities and towns within the state, and to all legal intents and purposes a "general law" within the meaning of Article 11, section 10 of the state Constitution, as amended.
If any provision of this title is in conflict with any provision of the charter or amendments thereto of any charter code city, the provisions of this title shall govern and control, except where the legislative body of such charter code city, by ordinance, elects to retain such charter provision or amendment, in which event such charter provision shall prevail notwithstanding a conflict with provisions of this optional code: PROVIDED, That such ordinance shall be subject to referendum as provided in RCW 35A.29.170.
RCW 35A.21.020