California Code, Welfare and Institutions Code - WIC § 6507

The court shall inquire into the condition or status of the person alleged to have a developmental disability.  For this purpose it may by subpoena require the attendance before it of a physician who has made a special study of developmental disabilities and is qualified as a medical examiner, and of a clinical psychologist, or of two such physicians, or of two such psychologists, to examine the person and testify concerning his or her developmental disability.  The court may also by subpoena require the attendance of such other persons as it deems advisable, to give evidence.