--- /dev/null
+<?php
+namespace Consolidation\OutputFormatters\StructuredData;
+
+use Consolidation\OutputFormatters\Options\FormatterOptions;
+
+/**
+ * UnstructuredInterface is a marker interface that indicates that the
+ * data type is unstructured, and has no default conversion to a string.
+ * Unstructured data supports the `string` format only if it also implements
+ * StringTransformationInterface.
+ */
+interface UnstructuredInterface
+{
+}