Added key regex

Author: darrelmiller

versions/3.0.md

@@ -400,7 +400,7 @@ Field Pattern | Type | Description
 <a name="linksDefinitionObject"></a> | [Link Definitions Object](#linksDefinitionsObject) | Link definitions to reuse across the specification.
 <a name="callbacksDefinitionObject"></a> | [Callback Definitions Object](#callbacksDefinitionsObject) | Callback definitions to reuse across the specification.
 
-All the fixed fields declared above are objects that MUST contain keys that only use the following characters: `a-zA-Z0-9.-_\`.
+All the fixed fields declared above are objects that MUST use keys that match the regular expression: `[a-zA-Z0-9.\-_]+`.
 
 #### <a name="pathsObject"></a>Paths Object