Merged in feature/from-pantheon (pull request #16)

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo/inc/sitemaps/interface-sitemap-cache-data.php

@@ -0,0 +1,72 @@
+<?php
+/**
+ * WPSEO plugin file.
+ *
+ * @package WPSEO\XML_Sitemaps
+ */
+
+/**
+ * Cache Data interface.
+ */
+interface WPSEO_Sitemap_Cache_Data_Interface {
+
+	/**
+	 * Status for normal, usable sitemap.
+	 *
+	 * @var string
+	 */
+	const OK = 'ok';
+
+	/**
+	 * Status for unusable sitemap.
+	 *
+	 * @var string
+	 */
+	const ERROR = 'error';
+
+	/**
+	 * Status for unusable sitemap because it cannot be identified.
+	 *
+	 * @var string
+	 */
+	const UNKNOWN = 'unknown';
+
+	/**
+	 * Set the content of the sitemap.
+	 *
+	 * @param string $sitemap The XML content of the sitemap.
+	 *
+	 * @return void
+	 */
+	public function set_sitemap( $sitemap );
+
+	/**
+	 * Set the status of the sitemap.
+	 *
+	 * @param bool|string $usable True/False or 'ok'/'error' for status.
+	 *
+	 * @return void
+	 */
+	public function set_status( $usable );
+
+	/**
+	 * Builds the sitemap.
+	 *
+	 * @return string The XML content of the sitemap.
+	 */
+	public function get_sitemap();
+
+	/**
+	 * Get the status of this sitemap.
+	 *
+	 * @return string Status 'ok', 'error' or 'unknown'.
+	 */
+	public function get_status();
+
+	/**
+	 * Is the sitemap content usable ?
+	 *
+	 * @return bool True if the sitemap is usable, False if not.
+	 */
+	public function is_usable();
+}