The purpose of this part is to supplement previously enacted provisions of law that authorize cities to levy assessments pursuant to the Parking and Business Improvement Area Law of 1989 (Part 6 (commencing with Section 36500)) and the Property and Business Improvement District Law of 1994 (Part 7 (commencing with Section 36600)). This part does not affect or limit any other provisions of law authorizing or providing for the furnishing of improvements or activities or the raising of revenue for these purposes.