d

history/history-network.md

@@ -213,22 +213,33 @@ This content type represents block headers *near* the HEAD of the chain.  They a
 
 > Note: This message is not valid for Gossip.  Clients should not send or accept gossip messages for this content type.
 
+> Note: Clients **should** implement a mechanism to purge headers older than 8192 blocks from their content databases.
+
 ```python
 # The maximum number of ephemeral headers that can be requested or transferred
 # in a single request.
 MAX_EPHEMERAL_HEADER_PAYLOAD = 256
 
 # Content and content key
 
-recent_headers = Container(block_hash: Bytes32, ancestor_count: uint8)
+ephemeral_headers_key = Container(block_hash: Bytes32, ancestor_count: uint8)
 selector         = 0x04
 
-block_header_list = List(ByteList[1024], limit=256)
+ephemeral_header_payload = List(ByteList[1024], limit=256)
 
-content          = SSZ.serialize(block_header_list)
-content_key      = selector + SSZ.serialize(recent_headers)
+content          = SSZ.serialize(ephemeral_header_payload)
+content_key      = selector + SSZ.serialize(ephemeral_headers_key)
 ```
 
+The `ephemeral_header_payload` is an SSZ list of RLP encoded block header
+objects.  The this object is subject to the following validity conditions.
+
+* The list **may** be empty which signals that the responding node was unable to fulfill the request.
+* The first element in the list **must** be the RLP encoded block header indicated by the `ephemeral_headers_key.block_hash` field from the content key.
+* Each element after the first element in the list **must** be the RLP encoded block header indicated by the `header.parent_hash` of the previous item from the list.
+* The list **should** contain no more than `ephemeral_headers_key.ancestor_count` items.
+
+
 #### Block Body
 
 After the addition of `withdrawals` to the block body in the [EIP-4895](https://eips.ethereum.org/EIPS/eip-4895),