From 53e75404372e8039028327335880fb0aabd52f17 Mon Sep 17 00:00:00 2001
From: Noah Treuhaft <noah.treuhaft@gmail.com>
Date: Wed, 18 Mar 2020 10:26:41 -0700
Subject: [PATCH] Limit sets to one primitive element in ZNG spec (#431)

This brings the spec in line with the implementation.
---
 zng/docs/spec.md | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/zng/docs/spec.md b/zng/docs/spec.md
index aa1a6f1325..b5793cc53c 100644
--- a/zng/docs/spec.md
+++ b/zng/docs/spec.md
@@ -255,15 +255,18 @@ the array encoded as a `uvarint`:
 
 #### 2.1.1.3 Set Typedef
 
-A set type is encoded as a concatenation of the type IDs that comprise
-the elements of the set where each type ID and the number of types
-in the set are all encoded as a `uvarint`:
+A set type is encoded as a type count followed by the type ID of the
+elements of the set, each encoded as a `<uvarint>`:
 ```
-----------------------------------------
-|0x82|<ntypes><type-id-1><type-id-2>...|
-----------------------------------------
+-------------------------
+|0x82|<ntypes>|<type-id>|
+-------------------------
 ```
 
+`<ntypes>` must be 1.
+
+`<type-id>` must be a primitive type ID.
+
 #### 2.1.1.4 Union Typedef
 
 A union typedef creates a new type ID equal to the next stream type ID
@@ -521,7 +524,7 @@ grammar describing the textual type encodings is:
           | record [ <columns> ]
           | record [ ]
           | union [ <stype-list> ]
-          | set [ <stype-list> ]
+          | set [ <stype> ]
 
 
 <stype-list> :=    <stype>