Legal research on censorship

I've been in and out of this prison law library and I've found some information that should be placed in the Under Lock and Key section of MIM Notes. According to the California Prisoners Rights Handbook, page 49:

Prison officials are permitted to open and read most incoming and outgoing mail, except legal or confidential mail that may not be read by prison staff. Such "regular" mail may be withheld or censored only when necessary for the reasonable protection of the public. Mail cannot be censored because prison officials believe it improperly magnifies complaints or contains inflammatory remarks. A prisoner should receive notice of any mail that is withheld or is returned.

I've studied other law books and prison officials taking our mail or sending it back is dead wrong. I've heard that the prisons and their officials are supposed to be letting us prisoners get our political books back, but it's just a rumor as I've heard. I will keep studying the law books.