style: whatever is defined by "teambalancestyle", generally a skill ranking method
number: try to keep an even balance of team player numbers (eg. avoid 4v2 and balance to 3v3)
enforce: players can't immediately change teams if it would result in unbalanced team player numbers (by default results in a swap request)
reassign: if teams become unbalanced, reassign players when available
The "6" value is a special one we are supposed to be using now (I guess we forgot to update it) used to force teams to be balanced by "style" during pre-round waiting, then reverting to "4" when the match starts. What this means is that teams are allowed to be unbalanced during pre-round if it means we sort according to style of all the participating players evenly (eg. skills will attempt to balance evenly between teams), once the match starts the server will then switch to reassigning players to make balanced team player numbers, generally picking from the bottom of the style pool in order to keep things as evenly matched as possible.