From a12f6df77772cc4c86b69e01d9e4ea7addb09dce Mon Sep 17 00:00:00 2001
From: Lee Byron <lee@leebyron.com>
Date: Thu, 16 Jul 2015 12:45:35 -0700
Subject: [PATCH] Add constraints to `EnumValue`

This changes the formatting for constraints to be a little easier to read IMO.

Also, adds the disambiguating constraints to `EnumValue`.
---
 Section 8 -- Grammar.md | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/Section 8 -- Grammar.md b/Section 8 -- Grammar.md
index 7b7aea944..7839f4a96 100644
--- a/Section 8 -- Grammar.md	
+++ b/Section 8 -- Grammar.md	
@@ -68,6 +68,24 @@ Example_param :
   - C_param
   - D
 
+A grammar production may specify that certain expansions are not permitted by
+using the phrase "but not" and then indicating the expansions to be excluded.
+
+For example, the production:
+
+SafeName : Name but not SevenCarlinWords
+
+means that the nonterminal {SafeName} may be replaced by any sequence of
+characters that could replace {Name} provided that the same sequence of
+characters could not replace {SevenCarlinWords}.
+
+A grammar may also list a number of restrictions after "but not" seperated
+by "or".
+
+For example:
+
+NonBooleanName : Name but not `true` or `false`
+
 
 ## Ignored Source
 
@@ -247,7 +265,7 @@ InlineFragment : ... on TypeCondition Directives? SelectionSet
 
 FragmentDefinition : fragment FragmentName on TypeCondition Directives? SelectionSet
 
-FragmentName : [ lookahead ! on ] Name
+FragmentName : Name but not `on`
 
 TypeCondition : TypeName
 
@@ -271,7 +289,7 @@ BooleanValue :
   - true
   - false
 
-EnumValue : Name
+EnumValue : Name but not `true`, `false` or `null`
 
 
 #### Array Value