The web site of the Washington State Legislature provides the following description of the WAC:
“Regulations of executive branch agencies are issued by authority of statutes. Like legislation and the Constitution, regulations are a source of primary law in Washington State. The WAC codifies the regulations and arranges them by subject or agency. The online version of the WAC is updated twice a month. Copies of the WAC as they existed each year since 2004 are available in the WAC archive.”