Altered Metadata Extension rules to be clear about the ERC-165 usage and the fact that URI events are for changes and not mandatory to output on a mint operation (if the ERC1155Metadata_URI interface is included).

EIPS/eip-1155.md

@@ -31,7 +31,8 @@ New functionality is possible with this design, such as transferring multiple to
 
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
 
-**Smart contracts implementing the ERC-1155 standard MUST implement the `ERC1155` and `ERC165` interfaces.**
+**Smart contracts implementing the ERC-1155 standard MUST implement all of the functions in the `ERC1155` interface.**
+**Smart contracts implementing the ERC-1155 standard MUST implement the ERC-165 `supportsInterface` function and MUST return the constant value `true` if `0xd9b67a26` is passed through the `interfaceID` argument.**
 
 ```solidity
 pragma solidity ^0.5.9;
@@ -148,8 +149,8 @@ interface ERC1155 /* is ERC165 */ {
 
 ### ERC-1155 Token Receiver
 
-Smart contracts **MUST** implement all the functions in this interface to accept transfers. See "Safe Transfer Rules" for further detail.
-Smart contracts **MUST** implement the ERC-165 `supportsInterface` function and signify support for this interface. See "ERC1155TokenReceiver ERC-165 rules" for further detail.
+**Smart contracts MUST implement all of the functions in the `ERC1155TokenReceiver` interface to accept transfers. See "Safe Transfer Rules" for further detail.**
+**Smart contracts MUST implement the ERC-165 `supportsInterface` function and signify support for the `ERC1155TokenReceiver` interface to accept transfers. See "ERC1155TokenReceiver ERC-165 rules" for further detail.**
 
 ```solidity
 pragma solidity ^0.5.9;
@@ -413,11 +414,14 @@ Example of such a URI: `https://token-cdn-domain/{id}.json` would be replaced wi
 
 #### Metadata Extensions
 
-The following optional extensions can be identified with the (ERC-165 Standard Interface Detection)[https://eips.ethereum.org/EIPS/eip-165].
+The optional `ERC1155Metadata_URI` extension can be identified with the (ERC-165 Standard Interface Detection)[https://eips.ethereum.org/EIPS/eip-165].
 
-Changes to the URI MUST emit the `URI` event if the change can be expressed with an event (i.e. it isn't dynamic). If the optional ERC1155Metadata_URI extension is included, the `uri` function SHOULD be used to retrieve values for which no event was emitted. The function MUST return the same value as the event if it was emitted.
-
-Note that if this extension is enabled: if the URI event is to be used for metadata uri's changes, it does not need to be emitted first at Mint time. Observer can fetch the metadata uri at mint time from the `uri` function.
+If the optional `ERC1155Metadata_URI` extension is included:
+* The ERC-165 `supportsInterface` function MUST return the constant value `true` if `0x0e89341c` is passed through the `interfaceID` argument.
+* _Changes_ to the URI MUST emit the `URI` event if the change can be expressed with an event (i.e. it isn't dynamic/programmatic).
+    - An implementation MAY emit the `URI` event during a mint operation but it is NOT mandatory. An observer MAY fetch the metadata uri at mint time from the `uri` function if it was not emitted.    
+* The `uri` function SHOULD be used to retrieve values if no event was emitted. 
+* The `uri` function MUST return the same value as the latest event for an `_id` if it was emitted.
 
 ```solidity
 pragma solidity ^0.5.9;