Constant MIXED_PREFERENCE_07 

const MIXED_PREFERENCE_07: &str = "Every Track has a single 'Object Forwarding Preference' and the \
                                   Original Publisher MUST NOT mix different forwarding \
                                   preferences within a single track. If a subscriber receives \
                                   different forwarding preferences for a track, it SHOULD close \
                                   the session with an error of 'Protocol Violation'.";