What is a seller's duty to disclose to the buyer of a property?

"Generally, where one party to a transaction has sole knowledge or access to material facts and knows that such facts are not known or reasonably discoverable by the other party, then a duty to disclose exists. [Citation.] In the context of a real estate transaction, [i]t is now settled in California that where the seller knows of facts materially affecting the value or desirability of the property . . . and also knows that such facts are not known to, or within the reach of the diligent attention and observation of the buyer, the seller is under a duty to disclose them to the buyer. [Citations.]' Undisclosed facts are material if they would have a significant and measurable effect on market value." (Shapiro v. Sutherland (1998) 64 Cal.App.4th 1534, 1544 (Shapiro).)