Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 43378)
+++ wp-includes/taxonomy.php	(working copy)
@@ -4548,3 +4548,27 @@
 
 	return $parent;
 }
+
+/**
+ * Determines whether a taxonomy is considered "viewable".
+ *
+ * For built-in taxonomies such as categories and tags, the 'public' value will be evaluated.
+ * For all others, the 'publicly_queryable' value will be used.
+ * *
+ * @param string|WP_Taxonomy $taxonomy Taxonomy name or object.
+ * @return bool Whether the taxonomy should be considered viewable.
+ */
+function is_taxonomy_viewable( $taxonomy ) {
+	if ( is_scalar( $taxonomy ) ) {
+		$taxonomy = get_taxonomy( $taxonomy );
+		if ( ! $taxonomy ) {
+			return false;
+		}
+	}
+
+	if ( ! isset( $taxonomy->publicly_queryable, $taxonomy->_builtin, $taxonomy->public ) ) {
+		return false;
+	}
+
+	return $taxonomy->publicly_queryable || ( $taxonomy->_builtin && $taxonomy->public );
+}