Under the "American rule" each party pays its own legal fees. This rule prevails absent explicit statutory authority. (Buckhannon Board & Care Home, Inc. v. West Virginia Dept. of Health and Human Resources (2001) 532 U.S. 598, 602.) One statutory exception to the rule is found in section 1988 of the federal Civil Rights Act: "In any action or proceeding to enforce a provision of section 1983 . . . the court, in its discretion, may allow the prevailing party, other than the United States, a reasonable attorney's fee as part of the costs." (42 U.S.C. 1988(b).) Claims for attorney fees under section 1988 "are available in any 1983 action." (Maine v. Thiboutot (1980) 448 U.S. 1, 9-10 (Maine).) This includes section 1983 actions that are filed in state court. (Maine, at p. 10.) Section 1983 provides in relevant part: "Every person who, under color of any statute, ordinance, regulation, custom, or usage, of any State or Territory . . . subjects, or causes to be subjected, any citizen of the United States or other person within the jurisdiction thereof to the deprivation of any rights, privileges, or immunities secured by the Constitution and laws, shall be liable to the party injured in an action at law, suit in equity, or other proper proceeding . . . ." (42 U.S.C. 1983.) To be eligible for section 1988 fees, a plaintiff need not prevail specifically on a section 1983 claim. (Filipino Accountants' Assn. v. State Bd. of Accountancy (1984) 155 Cal.App.3d 1023, 1032 (Filipino Accountants' Assn.).) If the plaintiff prevails on a claim not covered by section 1988, and the validity of the section 1983 claim was never adjudicated by the court, the plaintiff is still considered to be a prevailing party under section 1988 provided that (1) the non-fee claim and section 1983 claim both arose out of a " 'common nucleus of operative fact' "; and (2) the section 1983 claim is "substantial," meaning that it is not inescapably foreclosed by prior decisions. (Filipino Accountants' Assn., at pp. 1032-1034 42 U.S.C. 1981 claim, relying on Maher v. Gagne (1980) 448 U.S. 122, 132-133, fn. 15; White v. Beal (E.D.Pa. 1978) 447 F.Supp. 788, 793.) Allowing fees in such cases " 'furthers the Congressional goal of encouraging suits to vindicate constitutional rights without undermining the longstanding judicial policy of avoiding unnecessary decision of important constitutional issues.' " (Filipino Accountants' Assn., at p. 1033, quoting Maher v. Gagne, at pp. 132-133.) However, a plaintiff who prevails on a state law claim, but loses on a related section 1983 claim, is not considered a prevailing party for purposes of section 1988. (See Mateyko v. Felix (9th Cir. 1990) 924 F.2d 824, 828, and cases collected therein.)