Merge pull request #684 from ethereum/vbuterin-patch-5

Developer notice

specs/core/1_shard-data-chains.md

@@ -2,6 +2,8 @@
 
 **NOTICE**: This document is a work-in-progress for researchers and implementers. It reflects recent spec changes and takes precedence over the [Python proof-of-concept implementation](https://github.com/ethereum/beacon_chain).
 
+At the current stage, Phase 1, while fundamentally feature-complete, is still subject to change. Development teams with spare resources may consider starting on the "Shard chains and crosslink data" section; at least basic properties, such as the fact that a shard block can get created every slot and is dependent on both a parent block in the same shard and a beacon chain block at or before that same slot, are unlikely to change, though details are likely to undergo similar kinds of changes to what Phase 0 has undergone since the start of the year.
+
 ## Table of contents
 
 <!-- TOC -->
@@ -15,26 +17,27 @@
             - [Time parameters](#time-parameters)
             - [Max operations per block](#max-operations-per-block)
             - [Signature domains](#signature-domains)
-    - [Helper functions](#helper-functions)
+    - [Shard chains and crosslink data](#shard-chains-and-crosslink-data)
+      - [Helper functions](#helper-functions)
             - [`get_split_offset`](#get_split_offset)
             - [`get_shuffled_committee`](#get_shuffled_committee)
             - [`get_persistent_committee`](#get_persistent_committee)
             - [`get_shard_proposer_index`](#get_shard_proposer_index)
-    - [Data Structures](#data-structures)
+      - [Data Structures](#data-structures)
         - [Shard chain blocks](#shard-chain-blocks)
-    - [Shard block processing](#shard-block-processing)
+      - [Shard block processing](#shard-block-processing)
         - [Verifying shard block data](#verifying-shard-block-data)
         - [Verifying a crosslink](#verifying-a-crosslink)
         - [Shard block fork choice rule](#shard-block-fork-choice-rule)
-- [Updates to the beacon chain](#updates-to-the-beacon-chain)
-    - [Data structures](#data-structures)
+    - [Updates to the beacon chain](#updates-to-the-beacon-chain)
+      - [Data structures](#data-structures)
         - [`Validator`](#validator)
         - [`BeaconBlockBody`](#beaconblockbody)
         - [`BranchChallenge`](#branchchallenge)
         - [`BranchResponse`](#branchresponse)
         - [`BranchChallengeRecord`](#branchchallengerecord)
         - [`SubkeyReveal`](#subkeyreveal)
-    - [Helpers](#helpers)
+      - [Helpers](#helpers)
         - [`get_attestation_merkle_depth`](#get_attestation_merkle_depth)
         - [`epoch_to_custody_period`](#epoch_to_custody_period)
         - [`slot_to_custody_period`](#slot_to_custody_period)
@@ -42,13 +45,13 @@
         - [`verify_custody_subkey_reveal`](#verify_custody_subkey_reveal)
         - [`prepare_validator_for_withdrawal`](#prepare_validator_for_withdrawal)
         - [`penalize_validator`](#penalize_validator)
-    - [Per-slot processing](#per-slot-processing)
+      - [Per-slot processing](#per-slot-processing)
         - [Operations](#operations)
             - [Branch challenges](#branch-challenges)
             - [Branch responses](#branch-responses)
             - [Subkey reveals](#subkey-reveals)
-    - [Per-epoch processing](#per-epoch-processing)
-    - [One-time phase 1 initiation transition](#one-time-phase-1-initiation-transition)
+      - [Per-epoch processing](#per-epoch-processing)
+      - [One-time phase 1 initiation transition](#one-time-phase-1-initiation-transition)
 
 <!-- /TOC -->
 
@@ -98,6 +101,8 @@ Phase 1 depends upon all of the constants defined in [Phase 0](0_beacon-chain.md
 | `DOMAIN_SHARD_ATTESTER`| 130             |
 | `DOMAIN_CUSTODY_SUBKEY`| 131             |
 
+# Shard chains and crosslink data
+
 ## Helper functions
 
 #### `get_split_offset`