What are the elements of promissory estoppel?

"'Promissory estoppel is "a doctrine which employs equitable principles to satisfy the requirement that consideration must be given in exchange for the promise sought to be enforced."' [Citations.] The elements of promissory estoppel are (1) a clear promise, (2) reliance, (3) substantial detriment, and (4) damages 'measured by the extent of the obligation assumed and not performed.'" (Toscano v. Greene Music (2004) 124 Cal.App.4th 685, 692.)