In Dart Industries, Inc. v. Commercial Union Ins. Co. (2002) 28 Cal.4th 1059, the California Supreme Court addressed "what an insured must prove in order to establish its rights under a lost or destroyed insurance policy." (Id. at p. 1064.) The court held that "the claimant has the burden of proving (1) the fact that he or she was insured under the lost policy during the period in issue, and (2) the substance of each policy provision essential to the claim for relief, i.e. , essential to the particular coverage that the insured claims. . . . In turn, the insurer has the burden of proving the substance of any policy provision 'essential to the . . . defense' (Evid. Code, 500), i.e., any provision that functions to defeat the insured's claim. " (Id. at p. 1071.) In applying these principles, the Supreme Court held the proponent of the lost document "need only prove the relevant substance of the document" by secondary evidence of its material terms and need not prove the actual words. (Id. at p. 1073.) "When, as here, it is undisputed that there was an insurance policy covering the relevant time period and that the policy was lost in good faith and not recovered after diligent search, there is no reason either in the law of contract or of evidence why secondary evidence that attests to the substance but not the precise language of an insurance policy should be insufficient as a matter of law to establish the insurer's contractual obligations." (Id. at p. 1074.) In Dart, it was undisputed that there existed a comprehensive general liability insurance policy covering the insured during the relevant time period and that it had been lost. (Id. at p. 1072.) The dispute centered around the material provisions of that policy and whether secondary evidence could be used to prove the substance of those provisions where they were "custom tailored to the insured" rather than a standard form. (Id. at pp. 1067, 1073-1074.) The Court noted: "'Historically, "other insurance" clauses were designed to prevent multiple recoveries when more than one policy provided coverage for a particular loss.' On the other hand, 'other insurance' clauses that attempt to shift the burden away from one primary insurer wholly or largely to other insurers have been the objects of judicial distrust. 'Public policy disfavors "escape" clauses, whereby coverage purports to evaporate in the presence of other insurance. This disfavor should also apply, to a lesser extent, to excess-only clauses, by which carriers seek exculpation whenever the loss falls within another carrier's policy limit.' Partly for this reason, the modern trend is to require equitable contributions on a pro rata basis from all primary insurers regardless of the type of 'other insurance' clause in their policies. " (Id. at pp. 1079-1080.) The California Supreme Court acknowledged these principles, recognizing the "judicial distrust" of "other insurance" provisions that attempt to shift the burden away from one primary insurer partly or wholly to other insurers. " 'Public policy disfavors "escape" clauses, whereby coverage purports to evaporate in the presence of other insurance. This disfavor should also apply, to a lesser extent, to excess-only clauses, by which carriers seek exculpation whenever the loss falls within another carrier's policy limit.' " (Dart Industries, supra, 28 Cal.4th at p. 1080.) The Court said: "Partly for this reason, the modern trend is to require equitable contributions on a pro rata basis from all primary insurance regardless of the type of 'other insurance' clause in their policies." (Dart Industries, at p. 1080.)