userid_mark

If the parameter is not off, enables the cookie marking mechanism and sets the character used as a mark. This mechanism is used to add or change userid_p3p and/or a cookie expiration time while preserving the client identifier. A mark can be any letter of the English alphabet (case-sensitive), digit, or the “=” character.

If the mark is set, it is compared with the first padding symbol in the base64 representation of the client identifier passed in a cookie. If they do not match, the cookie is resent with the specified mark, expiration time, and “P3P” header.