2005 California Probate Code Sections 6130-6131 CHAPTER 4. REFERENCE TO MATTERS OUTSIDE THE WILL

6130.  A writing in existence when a will is executed may be
incorporated by reference if the language of the will manifests this
intent and describes the writing sufficiently to permit its
identification.
6131.  A will may dispose of property by reference to acts and
events that have significance apart from their effect upon the
dispositions made by the will, whether the acts and events occur
before or after the execution of the will or before or after the
testator's death.  The execution or revocation of a will of another
person is such an event.