(a)
When a case is appealed, there shall be no communication direct or indirect between the judge or judicial officer who heard the case and any judge of the reviewing court concerning the facts or merits of the case.(b)
When a petition for an original writ names a court as a party, there shall be no communication direct or indirect between any judge hearing the writ and the judge or judicial officer of the court named as a party.(c)
The prohibitions of subdivisions (a) and (b) shall not apply to a written communication if at the time the communication is transmitted all the parties are sent a copy.
Source:
Section 68070.5, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV§ionNum=68070.5..