[3] Section 580b, which limits the liability of purchasers of real property to the value of the security, was enacted in the interests of the general public. ( Roseleaf Corp. v. Chierighino, 59 Cal.2d 35 [ 27 Cal.Rptr. 873, 378 P.2d 97]; Brown v. Jensen, 41 Cal.2d 193 [ 259 P.2d 425]; Winklemen v. Sides, 31 Cal.App.2d 387 [ 88 P.2d 147]; California Bank v. Stimson, 89 Cal.App.2d 552 [ 201 P.2d 39]; Freedland v. Greco, 45 Cal.2d 462 [ 289 P.2d 463]; Riddle v. Lushing, supra, 203 Cal.App.2d 831; In re Wilton-Maxfield Management Co. (9th Cir. 1941) supra, 117 F.2d 913; Lucky Investments, Inc. v. Adams, 183 Cal.App.2d 462 [ 7 Cal.Rptr. 57]; Bargioni v. Hill, 59 Cal.2d 121 [ 28 Cal.Rptr. 321, 378 P.2d 593].) Freedland v. Greco, supra, 45 Cal.2d 462, was an appeal from a deficiency judgment after the sale of real property under a power of sale.

) The statutes were "adopted to promote the public welfare by shielding the debtor class from oppression." ( California Bank v. Stimson, 89 Cal.App.2d 552, 554 [ 201 P.2d 39].) They are to be "liberally construed to effectuate the specific legislative purpose behind [them].

The provisions of that section have been held to be part of a legislative plan to lighten the burdens of trust-debtors and they may not be waived as they are not mere personal rights for the benefit of individuals. ( Hatch v. Security-First Nat. Bank, 19 Cal.2d 254, 259 [ 120 P.2d 869]; California Bank v. Stimson, 89 Cal.App.2d 552, 554-555 [ 201 P.2d 39].) The time provided in the section is reasonable.

[5]In Brown v. Jensen, supra, 41 Cal.2d 193, 197, we held: "These provisions [Code Civ. Proc., §§ 580-580d, 726] indicate a considered course on the part of the Legislature to limit strictly the right to recover deficiency judgments, that is, to recover on the debt more than the value of the security." [6] Moreover, those provisions may not be waived in advance by the debtor as the courts have held with respect to section 726 of the Code of Civil Procedure ( Winklemen v. Sides, 31 Cal.App.2d 387 [ 88 P.2d 147] and section 580a ( California Bank v. Stimson, 89 Cal.App.2d 552 [ 201 P.2d 39]) and, see generally, Salter v. Ulrich, 22 Cal.2d 263 [ 138 P.2d 7, 146 A.L.R. 1344] and Morello v. Metzenbaum, 25 Cal.2d 494 [ 154 P.2d 670]. Because of the strong reasons of policy expressed in the Winklemen and California Bank cases the same rules should apply to section 580d The section would have little effect if the prospective creditor could compel the prospective debtor to waive it in advance.

In reaching our conclusion we are supported by cases that have interpreted section 580a as constituting a statute of limitations. (See, e.g., Citrus StateBank v. McKendrick (1989) 215 Cal.App.3d 941, 943; California Bank v. Stimson (1949) 89 Cal.App.2d 552; Ware v. Heller (1944) 63 Cal.App.2d 817, 823-825.) As does section 726, subdivision (b), which applies to judicial foreclosures, section 580a provides that in the case of non-judicial foreclosures, a creditor seeking a money judgment for a deficiency must bring an action seeking a deficiency judgment within three months of the sale of the security.

In some instances, the requirement that a statute of limitations defense be specifically pleaded is not applicable. Thus, in California Bank v. Stimson (1949) 89 Cal.App.2d 552, the question was whether the action was properly brought within the three-month period pescribed in Code of Civil Procedure section 580a, an anti-deficiency statute. The court held that the provision was one declarative of the public policy of the state to promote the public welfare by shielding mortgage and trust deed debtors, and that accordingly, it could not be waived by contract.

The salutary provisions of Section 580d are designed and intended to implement a statutory public policy ordained to protect debtors as a class against deficiency judgments in foreclosures. See California Bank v. Stimson, 1949, 89 Cal.App.2d ___, 201 P.2d 39. It is clear that the remedial and relief aspects of Section 580d are for the benefit and protection of mortgage and trust deed debtors and that its scope and purview should not be enlarged to diminish or impair rights of others.

Although certain antideficiency protections (e.g., Code Civ. Proc., § 580d) are applicable to guarantors, a guarantor may waive such defenses ( Union Bank v. Gradsky (1968) 265 Cal.App.2d 40, 48, 71 Cal.Rptr. 64; see also River Bank America v. Diller (1995) 38 Cal.App.4th 1400, 1415, 45 Cal.Rptr.2d 790), whereas a debtor may not. (Union Bank v. Wendland (1976) 54 Cal.App.3d 393, 408, 126 Cal.Rptr. 549;California Bank v. Stimson (1949) 89 Cal.App.2d 552, 554, 201 P.2d 39.) Where a contracting party is sufficiently aware of the circumstances and consequences of a waiver, contractual waiver/estoppel will be found: “[P]arties who have expressed their mutual assent are bound by the contents of the instrument they have signed, and may not thereafter claim that its provisions do not express their intentions or understanding.” ( City of Santa Cruz v. Pac. Gas & Elec. Co. (2000) 82 Cal.App.4th 1167, 1176, 99 Cal.Rptr.2d 198, citing Estate of Wilson (1976) 64 Cal.App.3d 786, 801–802, 134 Cal.Rptr. 749; see also Evid.Code, § 622.)

         A law has been established "for a public reason" only if it has been enacted for the protection of the public generally, i. e., if its tendency is to promote the welfare of the general public rather than a small percentage of citizens. 12 Am.Jur. 661; In re Kazas, 22 Cal.App.2d 161 ; California Bank v. Stimson, 89 Cal.App.2d 552 ; DeHaviland v. Warner Bros. Pictures, Inc., 67 Cal.App.2d 225 .         In California Bank v. Stimson, supra, it was held that Code of Civil Procedure, section 580a prescribing the procedure for securing a deficiency judgment was adopted to promote the public welfare by shielding the debtor class from oppression.