@0x/utils: Add docstring for raw constructor parameter in RevertError.

`@0x/utils`: Use `...is.instanceof()` pattern in `RevertError` tests.

packages/utils/CHANGELOG.json

@@ -14,6 +14,10 @@
                 "note": "Add `LibFixedMath` `RevertError` types.",
                 "pr": 2109
             },
+            {
+                "note": "Add `RawRevertError` `RevertError` type.",
+                "pr": 2109
+            },
             {
                 "note": "Make `RevertError.decode()` optionally return a `RawRevertError` if the selector is unknown.",
                 "pr": 2109

packages/utils/src/revert_error.ts

@@ -145,6 +145,9 @@ export abstract class RevertError extends Error {
      * Parameters that are left undefined will not be tested in equality checks.
      * @param declaration Function-style declaration of the revert (e.g., Error(string message))
      * @param values Optional mapping of parameters to values.
+     * @param raw Optional encoded form of the revert error. If supplied, this
+     *        instance will be treated as a `RawRevertError`, meaning it can only
+     *        match other `RawRevertError` types with the same encoded payload.
      */
     protected constructor(name: string, declaration?: string, values?: ValueMap, raw?: string) {
         super(createErrorMessage(name, values));

packages/utils/test/revert_error_test.ts

@@ -146,7 +146,7 @@ describe('RevertError', () => {
         it('should decode an unknown selector as a `RawRevertError`', () => {
             const _encoded = encoded.substr(0, 2) + '00' + encoded.substr(4);
             const decoded = RevertError.decode(_encoded, true);
-            expect(decoded instanceof RawRevertError).to.be.true();
+            expect(decoded).is.instanceof(RawRevertError);
         });
         it('should fail to decode a malformed ABI encoded revert error', () => {
             const _encoded = encoded.substr(0, encoded.length - 1);