A soulbound badge is a token that, when minted, is bound to another Non-Fungible Token (NFT), and cannot be transferred/moved after that.
Implementers of this standard SHOULD also depend on a standard for interface detection so callers can easily find out if a given contract implements this interface.
By requiring that badges can never move, we both guarantee non-separability and non-mergeability among collections of soulbound badges that are bound to a single NFT while simultaneously allowing users to aggressively cache results.
Soulbound badges are meant to be permanent badges/indicators attached to a persona. This means that not only can the user not transfer ownership, but the minter also cannot withdraw/transfer/change ownership as well. This includes mutating or removing any remote content as a means of censoring or manipulating specific users.
badgeUri Data FormatThe format of the data pointed to by collectionUri() and badgeUri(uint256), and how to merge them, is intentionally left out of this standard in favor of separate standards that can be iterated on in the future.
The immutability constraints are the only thing defined by this to ensure that the spirit of this badge is maintained, regardless of the specifics of the data format.
The metadataFormat function can be used to inform a caller what type/format/version of data they should expect at the URIs, so the caller can parse the data directly without first having to deduce its format via inspection.
This is a new token type and is not meant to be backward compatible with any existing tokens other than existing viable souls (any asset that can be identified by [address,id]).
Users of badges that claim to implement this EIP must be diligent in verifying they actually do. A badge author can create a badge that, upon initial probing of the API surface, may appear to follow the rules when in reality it doesn't. For example, the contract could allow transfers via some mechanism and simply not utilize them initially.
It should also be made clear that soulbound badges are not bound to a human, they are bound to a persona. A persona is any actor (which could be a group of humans) that collects multiple soulbound badges over time to build up a collection of badges. This persona may transfer to another human, or to another group of humans, and anyone interacting with a persona should not assume that there is a single permanent human behind that persona.
It is possible for a soulbound badge to be bound to another soulbound badge. In theory, if all badges in the chain are created at the same time they could form a loop. Software that tries to walk such a chain should take care to have an exit strategy if a loop is detected.
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