Rebinding is an uncommon role, but is still required to ensure the proper functioning of the protocol. Rebinders handle tokens that are left in a Bundle, but not associated with the index asset. This may result when the weight of an underlying token is changed to 0, or unsupported tokens are sent to the contract. Specifically, a Rebinder will call a Bundle's Unbinder contract, converting and swapping the unbound token back to the fund for a small reward. Note that this is once again a somewhat technical role, but is ultimately fairly straightforward.