--- /dev/null
+<?php
+
+namespace Drupal\metatag_open_graph\Plugin\metatag\Tag;
+
+use \Drupal\metatag\Plugin\metatag\Tag\MetaPropertyBase;
+
+/**
+ * The Open Graph "Book tag" meta tag.
+ *
+ * @MetatagTag(
+ * id = "book_tag",
+ * label = @Translation("Book tag(s)"),
+ * description = @Translation("Appropriate keywords for this content."),
+ * name = "book:tag",
+ * group = "open_graph",
+ * weight = 38,
+ * type = "label",
+ * secure = FALSE,
+ * multiple = TRUE
+ * )
+ */
+class BookTag extends MetaPropertyBase {
+ // Nothing here yet. Just a placeholder class for a plugin.
+}