--- /dev/null
+<?php
+
+namespace Drupal\datetime\Plugin\Field\FieldType;
+
+/**
+ * Interface definition for Datetime items.
+ */
+interface DateTimeItemInterface {
+
+ /**
+ * Defines the timezone that dates should be stored in.
+ */
+ const STORAGE_TIMEZONE = 'UTC';
+
+ /**
+ * Defines the format that date and time should be stored in.
+ */
+ const DATETIME_STORAGE_FORMAT = 'Y-m-d\TH:i:s';
+
+ /**
+ * Defines the format that dates should be stored in.
+ */
+ const DATE_STORAGE_FORMAT = 'Y-m-d';
+
+}