This mainly applies to Feature Characters but to be fair to all, it will be minimally required of Original Characters as well.
Engagements and weddings between characters are serious alterations to that character. Just as it is a serious institution in our society/culture, so it is on the game as we are based on the real world in most ways. You can have your Feature Character develop feelings for another character (Feature or Original) but you must inform staff prior to ever playing out a proposal.
The reason for this is simple. If for some reason, you are unable to continue playing your Feature Character, the repercussions of such an engagement/marriage will have to be dealt with by a new player in the future. Staff must know of such things to inform new applicants. If you wish to have your character become engaged (either to another Feature or Original character), submit a +request with your intentions so that they may be approved. There are times this may be denied but they are considered on a case-by-case basis.
For weddings (after the engagement is approved and played out), @mail in a TP proposal, as these are often big events which would include involvement of others in your RP sphere of play and thus require a TP to be completed.