What is the authority of a district attorney to decide whether to bring criminal charges?

'The decision as to appropriate charges is a matter of prosecutorial discretion. "[P]rosecutorial discretion is basic to the framework of the California criminal justice system. [Citations.] This discretion, though recognized by statute in California, is founded upon constitutional principles of separation of powers and due process of law." ' [Citations.] 'The district attorney's function is quasi-judicial in nature [citation], and . . . he is vested with discretionary power in determining whether to prosecute in any particular case. An unbroken line of cases in California has recognized this discretion and its insulation from control by the courts. . . .' [Citation, italics added.]" (Gananian v. Wagstaffe (2011) 199 Cal.App.4th 1532, 1543.)