What is the test for intentional waiver of a right?

"Case law is clear that ' "[w]aiver is the intentional relinquishment of a known right after knowledge of the facts." [Citations.] The burden ... is on the party claiming a waiver of a right to prove it by clear and convincing evidence that does not leave the matter to speculation, and "doubtful cases will be decided against a waiver" [citation].' [Citations.] The waiver may be either express, based on the words of the waiving party, or implied, based on conduct indicating an intent to relinquish the right. [Citation.]" (Waller v. Truck Ins. Exchange, Inc. (1995) 11 Cal.4th 1, 31, 44 Cal.Rptr.2d 370, 900 P.2d 619.)