explicit language about the ephemeral_headers_key validity

history/history-network.md

@@ -67,9 +67,6 @@ List of currently supported payloads, by latest to oldest.
 -  [Type 2 History Radius Payload](../ping-payload-extensions/extensions/type-2.md)
 
 
-* The `data_radius` value defines the *distance* from the node's node-id for which other clients may assume the node would be interested in content.
-* The `ephemeral_header_count` value defines the number of *recent* headers that this node stores.  The maximum effective value for this is 8192.
-
 ### Routing Table
 
 The history network uses the standard routing table structure from the Portal Wire Protocol.
@@ -262,6 +259,11 @@ content                  = SSZ.serialize(ephemeral_header_payload)
 content_key              = selector + SSZ.serialize(ephemeral_headers_key)
 ```
 
+The `ephemeral_headers_key` encodes a request for headers anchored to the block
+hash indicated by `ephemeral_headers_key.block_hash`.  The
+`ephemeral_headers_key.ancestor_count` **MUST** be in the inclusive range
+0-255.
+
 The `ephemeral_header_payload` is an SSZ list of RLP encoded block header
 objects.  The this object is subject to the following validity conditions.