enum for existence values

src/Enumerators/SchemaFieldExistence.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Darksparrow\DeegraphPHP\Enumerators;
+
+enum SchemaFieldExistence: string
+{
+    case MUST = "MUST";
+    case SHOULD = "SHOULD";
+    case MAY = "MAY";
+}