1 files changed, 66 insertions, 13 deletions

diff --git a/packages/contracts/src/2.0.0/tokens/ERC20Token/ERC20Token.sol b/packages/contracts/src/2.0.0/tokens/ERC20Token/ERC20Token.sol
index d9950145d..5ef5ee7ce 100644
--- a/packages/contracts/src/2.0.0/tokens/ERC20Token/ERC20Token.sol
+++ b/packages/contracts/src/2.0.0/tokens/ERC20Token/ERC20Token.sol
@@ -21,15 +21,21 @@ pragma solidity 0.4.24;
 import "./IERC20Token.sol";
 
 
-contract ERC20Token is IERC20Token {
+contract ERC20Token is
+    IERC20Token
+{
 
     mapping (address => uint256) internal balances;
     mapping (address => mapping (address => uint256)) internal allowed;
 
-    uint256 public totalSupply;
+    uint256 internal _totalSupply;
 
+    /// @dev send `value` token to `to` from `msg.sender`
+    /// @param _to The address of the recipient
+    /// @param _value The amount of token to be transferred
+    /// @return True if transfer was successful
     function transfer(address _to, uint256 _value)
-        public
+        external
         returns (bool)
     {
         require(
@@ -38,16 +44,32 @@ contract ERC20Token is IERC20Token {
         );
         require(
             balances[_to] + _value >= balances[_to],
-            "OVERFLOW"
+            "UINT256_OVERFLOW"
         );
+
         balances[msg.sender] -= _value;
         balances[_to] += _value;
-        emit Transfer(msg.sender, _to, _value);
+
+        emit Transfer(
+            msg.sender,
+            _to,
+            _value
+        );
+
         return true;
     }
 
-    function transferFrom(address _from, address _to, uint256 _value)
-        public
+    /// @dev send `value` token to `to` from `from` on the condition it is approved by `from`
+    /// @param _from The address of the sender
+    /// @param _to The address of the recipient
+    /// @param _value The amount of token to be transferred
+    /// @return True if transfer was successful
+    function transferFrom(
+        address _from,
+        address _to,
+        uint256 _value
+    )
+        external
         returns (bool)
     {
         require(
@@ -60,34 +82,65 @@ contract ERC20Token is IERC20Token {
         );
         require(
             balances[_to] + _value >= balances[_to],
-            "OVERFLOW"
+            "UINT256_OVERFLOW"
         );
+
         balances[_to] += _value;
         balances[_from] -= _value;
         allowed[_from][msg.sender] -= _value;
-        emit Transfer(_from, _to, _value);
+    
+        emit Transfer(
+            _from,
+            _to,
+            _value
+        );
+    
         return true;
     }
 
+    /// @dev `msg.sender` approves `_spender` to spend `_value` tokens
+    /// @param _spender The address of the account able to transfer the tokens
+    /// @param _value The amount of wei to be approved for transfer
+    /// @return Always true if the call has enough gas to complete execution
     function approve(address _spender, uint256 _value)
-        public
+        external
         returns (bool)
     {
         allowed[msg.sender][_spender] = _value;
-        emit Approval(msg.sender, _spender, _value);
+        emit Approval(
+            msg.sender,
+            _spender,
+            _value
+        );
         return true;
     }
 
+    /// @dev Query total supply of token
+    /// @return Total supply of token
+    function totalSupply()
+        external
+        view
+        returns (uint256)
+    {
+        return _totalSupply;
+    }
+
+    /// @dev Query the balance of owner
+    /// @param _owner The address from which the balance will be retrieved
+    /// @return Balance of owner
     function balanceOf(address _owner)
-        public
+        external
         view
         returns (uint256)
     {
         return balances[_owner];
     }
 
+    /// @param _owner The address of the account owning tokens
+    /// @param _spender The address of the account able to transfer the tokens
+    /// @return Amount of remaining tokens allowed to spent
     function allowance(address _owner, address _spender)
-        public
+        external
         view
         returns (uint256)
     {