From 1d613bab257aaa1c8013aaed54c5e608c53cad3b Mon Sep 17 00:00:00 2001
From: William Entriken <github.com@phor.net>
Date: Fri, 16 Feb 2018 14:18:18 -0500
Subject: [PATCH] Specify functions that cannot throw

---
 EIPS/eip-721.md | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/EIPS/eip-721.md b/EIPS/eip-721.md
index 015e31cc..cb8882c7 100644
--- a/EIPS/eip-721.md
+++ b/EIPS/eip-721.md
@@ -77,6 +77,7 @@ interface ERC721 /* is ERC165 */ {
 
     /// @notice Count all deeds assigned to an owner
     /// @dev Throws if `_owner` is the zero address, representing invalid deeds.
+    ///  Otherwise this function must not throw.
     /// @param _owner An address where we are interested in deeds owned by them
     /// @return The number of deeds owned by `_owner`, possibly zero
     function countOfDeedsByOwner(address _owner) external view returns (uint256 _count);
@@ -84,6 +85,7 @@ interface ERC721 /* is ERC165 */ {
     /// @notice Enumerate deeds assigned to an owner
     /// @dev Throws if `_index` >= `countOfDeedsByOwner(_owner)` or if
     ///  `_owner` is the zero address, representing invalid deeds.
+    ///  Otherwise this must not throw.
     /// @param _owner An address where we are interested in deeds owned by them
     /// @param _index A counter less than `countOfDeedsByOwner(_owner)`
     /// @return The identifier for the `_index`th deed assigned to `_owner`,
@@ -194,18 +196,21 @@ interface ERC721Enumerable {
     //     this.ownerByIndex.selector;
 
     /// @notice Enumerate active deeds
-    /// @dev Throws if `_index` >= `countOfDeeds()`
+    /// @dev Throws if `_index` >= `countOfDeeds()`.
+    ///  Otherwise must not throw.
     /// @param _index A counter less than `countOfDeeds()`
     /// @return The identifier for the `_index`th deed, (sort order not
     ///  specified)
     function deedByIndex(uint256 _index) external view returns (uint256 _deedId);
 
     /// @notice Count of owners which own at least one deed
+    ///  Must not throw.
     /// @return A count of the number of owners which own deeds
     function countOfOwners() external view returns (uint256 _count);
 
     /// @notice Enumerate owners
     /// @dev Throws if `_index` >= `countOfOwners()`
+    ///  Otherwise must not throw.
     /// @param _index A counter less than `countOfOwners()`
     /// @return The address of the `_index`th owner (sort order not specified)
     function ownerByIndex(uint256 _index) external view returns (address _owner);
@@ -215,7 +220,7 @@ interface ERC721Enumerable {
 Here is a also an optional **ERC-721 Operators Extension** for delegating access to your deeds. This is copied from the ERC-777 efforts. At this time DO NOT recommend this extension because of [a security considuration](https://github.com/ethereum/EIPs/issues/777#issuecomment-366182824) but we are putting it forth as a starting point for discussion.
 
 ```solidity
-/// WARNING: THIS INTERFACE IS TO PROMOTO DISCUSSION, WE DO NOT RECOMMEND YOU
+/// WARNING: THIS INTERFACE IS TO PROMOTE DISCUSSION, WE DO NOT RECOMMEND YOU
 /// IMPLEMENT IT YET AS THERE ARE SECURITY CONSIDERATIONS
 /// @title Delegated operator extension to ERC-721 interface
 /// @author William Entriken (https://phor.net)