> For the complete documentation index, see [llms.txt](https://docs.t-rex.network/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.t-rex.network/resources/faq.md).

# FAQ

Short answers to common questions. Each answer names the page that gives the full one.

### The protocol

**What is the T-REX protocol?** A set of smart contracts that records who owns a financial instrument, by identity, and enforces on every movement that the recipient may hold it and that the movement respects the rules of the asset. See [Protocol at a glance](/start-here/protocol-at-a-glance.md).

**How does it relate to ERC-3643?** T-REX is the reference implementation of ERC-3643. Version 5 keeps the interfaces of the standard and adds identity-based ownership, modular compliance and cross-chain distribution around them. See [T-REX and ERC-3643](/the-primary-register/t-rex-and-erc-3643.md).

**Is a T-REX token an ERC-20?** Yes. `transfer`, `approve`, `transferFrom` and `balanceOf` behave as a wallet or a contract expects. A transfer also passes the pause, the freezes, the eligibility of the recipient and the rules of the asset, and reverts if one refuses. See [The permissioned token](/token-and-register/the-permissioned-token.md).

**Is the protocol tied to one chain?** No. The protocol defines a reference chain by its role: it holds the register of every asset and every identity. Nothing in the contracts depends on which chain plays that role. See [The T-REX Ledger and its satellites](/cross-chain-the-distributed-register/the-t-rex-ledger-and-its-satellites.md).

**Is the code open source?** Yes. Both codebases are published under GPL-3.0. See [Changelog](/resources/changelog.md) for the repositories.

**Has it been audited?** ONCHAINID 3.0.0 was audited by OpenZeppelin. The audit of T-REX 5 is in progress. See [Audits and verification](/security-and-trust-model/audits-and-verification.md).

### Identity and eligibility

**Does every holder need an ONCHAINID?** Yes. Ownership and eligibility are evaluated on an identity. A holder either holds tokens at the address of its ONCHAINID, or at a wallet linked to it. See [An identity that is also an account](/identity-onchainid/an-identity-that-is-also-an-account.md).

**Can one Investor use several wallets?** Yes. Every wallet linked to an identity counts toward the same position, on any chain. A movement between two wallets of one identity changes no ownership. See [07 Link a wallet to an ONCHAINID](/guides/identity/07.-link-a-wallet-to-an-onchainid.md).

**Is personal data stored on-chain?** No. A claim carries a topic, validity dates and a payload that is a hash or an encoded value. The verification itself stays with the Claim Issuer. See [Claims: issuance, validity, revocation](/identity-onchainid/claims-issuance-validity-revocation.md).

**What is the difference between eligibility and compliance?** Eligibility says whether an identity may hold the asset: it has the claims the asset requires, from Claim Issuers the asset trusts. Compliance says whether one movement is allowed now: the modules of the asset decide. A movement passes both. See [Eligibility and compliance: the two gates](/the-primary-register/eligibility-and-compliance-the-two-gates.md).

**What happens when a claim expires or is revoked?** The holder keeps what it holds and can still send. It can no longer receive the assets that relied on that claim, until it holds a valid claim again. See [19 Revoke a claim](/guides/claim-issuer/19.-revoke-a-claim.md).

**What if a holder loses a wallet, or the keys of its identity?** For a lost wallet, a Token Agent moves the balance to a new address of the same identity: [15 Recover a lost wallet](/guides/agents/15.-recover-a-position-from-a-lost-wallet.md). For lost identity keys, the Guardians of the identity give it a new key: [21 Recover access to an ONCHAINID](/guides/identity/21.-recover-access-to-an-onchainid.md).

### Issuers

**What does an Issuer need to launch an asset?** A token suite, the claim topics it requires, the Claim Issuers it trusts, its compliance rules, and agents with their roles. See [J1 Issuer journey: launch an asset](/guides/journeys/j1.-issuer-journey-launch-an-asset.md).

**Can an Issuer write its own compliance rule?** Yes. A rule is a module bound to the compliance of the asset. See [Write a compliance module](/build/write-a-compliance-module.md).

**Who can upgrade the contracts of an asset?** For a suite on the shared beacons, the holder of the `VERSION_MANAGER` role of the network. For an isolated suite, the Issuer. See [Upgradeability: beacons and versions](/governance-and-infrastructure/upgradeability-beacons-and-versions.md).

**What can an Issuer do to a position without the holder?** Its agents can freeze an address or an amount, force a transfer, recover a balance to another address of the holder, burn, and pause the asset. Each is a separate role. See [Lifecycle controls](/token-and-register/lifecycle-controls.md).

**Can several assets share the same Investors?** Yes. Identities and their wallet links are global, and an Issuer can wire several assets to one identity storage. Each asset keeps its own required topics, trusted issuers and rules. See [IdentityRegistryStorage](/reference/token-suite/identityregistrystorage.md).

### Cross-chain

**Where is ownership recorded when tokens are on another chain?** On the reference chain. A position that is active on a satellite is recorded there as bridged, per wallet. `totalSupply` counts the whole issuance, satellites included. See [The balance model](/token-and-register/the-balance-model.md).

**How does a transfer on a satellite work?** The reference chain issues a validation for the transfer, after checking eligibility and the rules. The satellite executes only against that validation, and reports the execution. The register then records the change of ownership. See [31 Transfer on a satellite](/guides/cross-chain/31.-transfer-on-a-satellite.md).

**What if a message between chains is delayed or lost?** A validation that is not executed expires and is discarded, and its reservation is released. A report that arrives late is applied and flagged. See [36 Handle a late reconciliation or a halt](/guides/cross-chain/36.-handle-a-late-reconciliation-or-a-halt.md).

**Which messaging provider does the protocol use?** The protocol calls the ERC-7786 gateway interface and nothing below it. Chainlink is the default provider, and an Issuer can route a chain through any gateway the network trusts. See [Messaging providers](/cross-chain-the-distributed-register/messaging-providers.md).

### Developers

**Where do I start?** With the [Quickstart](/build/quickstart.md): get the code, run the tests, and write a first test against a complete local suite.

**Which packages do I install?** `@t-rex-network/t-rex` for the token suite and `@t-rex-network/onchainid` for the identity layer.

**How do I tell a holder why a transfer would fail?** With `UtilityChecker`, before the holder signs. See [Pre-flight checks with UtilityChecker](/build/pre-flight-checks-with-utilitychecker.md).

**Where are the contract addresses?** In [Deployments](/resources/deployments.md). The contracts of one asset are read from its token.

**I integrate ERC-3643 v4 today. What changes?** See [Coming from ERC-3643 v4](/start-here/coming-from-erc-3643-v4.md).


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