diff --git a/framework/validators/SafeValidator.php b/framework/validators/SafeValidator.php
index 846d63e68a..a7d31263ba 100644
--- a/framework/validators/SafeValidator.php
+++ b/framework/validators/SafeValidator.php
@@ -10,6 +10,14 @@ namespace yii\validators;
 /**
  * SafeValidator serves as a dummy validator whose main purpose is to mark the attributes to be safe for massive assignment.
  *
+ * This class is required because of the way in which Yii determines whether a property is safe for massive assignment, that is,
+ * when a user submits form data to be loaded into a model directly from the POST data, is it ok for a property to be copied.
+ * In many cases, this is required but because sometimes properties are internal and you do not want the POST data to be able to 
+ * override these internal values (especially things like database row ids), Yii assumes all values are unsafe for massive assignment
+ * unless a rule exists for the property, which in most cases it will. Sometimes, however, an item is safe for massive assigment but
+ * does not have a rule associated with it - for instance, due to no validation being performed, in which case, you use this class
+ * as a rule for that property. Although it has no functionality, it allows Yii to determine that the property is safe to copy.
+ * 
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */