Protocol types

The data-model layer of the specification: the containers, enumerations, and value types every other section operates on. Definitions here carry no execution semantics — validation rules, gas accounting, and the state transition itself live in the operative sections that consume these types.

Almost every rule in the specification is conditional on the active protocol fork, so the layer starts with the fork enumeration and the chain parameters that select it:

• Protocol forks — the ordered fork enumeration and its comparisons.
• Chain configuration — the activation schedule and chain identity a block is validated against.

The protocol containers follow (YP §4): accounts and storage, transactions, logs, and receipts, and block types. The execution engine's own types come next — EVM execution types and the system addresses and topics reserved by protocol upgrades.

The remaining pages define the byte-level and serialization-facing vocabulary: typed byte regions, code, cryptographic primitives, RLP field references, SSZ collections, and the stateless input envelope.