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# Modifications in Capella
## The gossip domain: gossipsub
A new topic is added to support the gossip of bls to execution change messages.
### Topics and messages
Topics follow the same specification as in prior upgrades. All topics remain stable except the beacon block topic which is updated with the modified type.
The new topics along with the type of the `data` field of a gossipsub message are given in this table:
Note that the `ForkDigestValue` path segment of the topic separates the old and the new `beacon_block` topics.
#### Global topics
Capella changes the type of the global beacon block topic and adds one global topic to propagate bls to execution change messages to all potential proposers of beacon blocks.
##### `beacon_block`
The *type* of the payload of this topic changes to the (modified) `SignedBeaconBlock` found in Capella.
Specifically, this type changes with the addition of `bls_to_execution_changes` to the inner `BeaconBlockBody`.
See Capella [state transition document](./beacon-chain.md#beaconblockbody) for further details.
##### `bls_to_execution_change`
This topic is used to propagate signed bls to execution change messages to be included in future blocks.
The following validations MUST pass before forwarding the `signed_bls_to_execution_change` on the network:
- _[IGNORE]_ The `signed_bls_to_execution_change` is the first valid signed bls to execution change received
for the validator with index `signed_bls_to_execution_change.message.validator_index`.
- _[REJECT]_ All of the conditions within `process_bls_to_execution_change` pass validation.
### Transitioning the gossip
See gossip transition details found in the [Altair document](../altair/p2p-interface.md#transitioning-the-gossip) for
details on how to handle transitioning gossip topics for Capella.
