ERC-3525 standardizes semi-fungibility through an <ID, SLOT, VALUE> model rather than through whole-contract balance accounting.
The slot is the key grouping primitive: tokens with the same slot keep unique IDs but can exchange fungible value.
The standard adds two especially important transfer modes: token-to-token value transfer within one slot, and token-to-address value transfer that resolves into a same-slot receiving token.
Approval becomes multi-layered: full-token authority, optional slot-level authority, and explicit value-level authority can all coexist.
Optional slot enumeration makes the semi-fungible namespace discoverable rather than leaving group structure entirely implicit.
Solv’s README makes the intended design space clearer than the EIP alone by emphasizing fractionalization, combination, computability, token nesting, programmable lockups, and structured-finance use cases.
Specific source signals worth retaining
EIP abstract and motivation: strongest sources for why the authors thought ERC-20 and ERC-721 each left a gap for quantity-carrying unique assets.
EIP transfer and approval sections: best sources for how semi-fungibility actually works operationally rather than rhetorically.
Slot enumeration and slot approval extensions: useful for understanding where discoverability and delegated control can sit in implementations.
Solv README: useful narrative source for why ERC-3525 became a structured-product and SFT primitive rather than only an NFT curiosity.
SFT white paper link: useful as the ecosystem-authored framing document even though the canonical standard remains the EIP.
Why this entry belongs in the corpus
It gives the tokenization cluster a clean lower-layer comparison point for semi-fungibility, tokenized balances, and quantity-carrying NFTs.
It helps separate slot-defined fungibility from partition-based rights segmentation and from bond-style class/nonce obligation modeling.
The durable insight is that many tokenized assets need both identity and quantity at once, and ERC-3525 makes that coexistence legible at the standard level.