propertyName must be required in the schema

Author: jdesrosiers

versions/3.1.1.md

@@ -2710,7 +2710,7 @@ names in "A" aren't considered when evaluating the referenced schema in "B".
 ##### Fixed Fields
 Field Name | Type | Description
 ---|:---:|---
-<a name="propertyName"></a>propertyName | `string` | **REQUIRED**. The name of the property in the payload that will hold the discriminator value.
+<a name="propertyName"></a>propertyName | `string` | **REQUIRED**. The name of the property in the payload that will hold the discriminator value. This property MUST be required in the payload schema.
 <a name="discriminatorMapping"></a> mapping | Map[`string`, `string`] | An object to hold mappings between payload values and schema names or references.
 
 This object MAY be extended with [Specification Extensions](#specificationExtensions).