diff --git a/lib/attribute.js b/lib/attribute.js
index 4ac88ac..54c998a 100644
--- a/lib/attribute.js
+++ b/lib/attribute.js
@@ -476,6 +476,7 @@ validators.multipleOf = function validateMultipleOf (instance, schema, options,
 validators.required = function validateRequired (instance, schema, options, ctx) {
   var result = new ValidatorResult(instance, schema, options, ctx);
   if (instance === undefined && schema.required === true) {
+    // A boolean form is implemented for reverse-compatability with schemas written against older drafts
     result.addError({
       name: 'required',
       message: "is required"