EIP-884 added isHolder function to proposed interface

EIPS/eip-884-DRAFT-DGCL-token.md

@@ -217,6 +217,13 @@ This will be extended as follows:
          */
         function isVerified(address addr) public view returns (bool);
 
+        /**
+         *  Checks to see if the supplied address is a stock holder.
+         *  @param addr The address to check.
+         *  @return true if the supplied address owns a token.
+         */
+        function isHolder(address addr) public view returns (bool);
+
         /**
          *  Checks that the supplied hash is associated with the given address.
          *  @param addr The address to test.
@@ -263,6 +270,8 @@ The SEC has additional requirements as to how a Crowdsale ought to be run and wh
 
 For example: The SEC requires a Crowdsale's website display the amount of money raised in USD. To support this a Crowdsale contract minting these Tokens must maintain a USD to ETH conversion rate (via Oracle or some other mechanism) and must record the conversion rate used at time of minting.
 
+Also, depending on the type of raise, the SEC (or other statutory body) can apply limits to the number of shareholders allowed. To support this the standard provides the `holderCount` and `isHolder` functions which a crowdsale can invoke to check that limits have not been exceeded.
+
 ### Use of the Identity `hash` value.
 
 Implementers of a Crowdsale, in order to comply with The Act, must be able to produce an up-to-date list of the names and addresses of all stockholders. It is not desirable to include those details in a public blockchain, both for reasons of privacy, and also for reasons of economy. Storing arbitrary string data on the blockchain is strongly discouraged.