Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/lib/Drupal/Component/Render/OutputStrategyInterface.php

@@ -0,0 +1,36 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Render\OutputStrategyInterface.
+ */
+
+namespace Drupal\Component\Render;
+
+/**
+ * Provides an output strategy that formats HTML strings for a given context.
+ *
+ * Output strategies assist in transforming HTML strings into strings that are
+ * appropriate for a given context (e.g. plain-text), through performing the
+ * relevant formatting. No santization is applied.
+ */
+interface OutputStrategyInterface {
+
+  /**
+   * Transforms a given HTML string into to a context-appropriate output string.
+   *
+   * This transformation consists of performing the formatting appropriate to
+   * a given output context (e.g., plain-text email subjects, HTML attribute
+   * values).
+   *
+   * @param string|object $string
+   *   An HTML string or an object with a ::__toString() magic method returning
+   *   HTML markup. The source HTML markup is considered ready for output into
+   *   HTML fragments and thus already properly escaped and sanitized.
+   *
+   * @return string
+   *   A new string that is formatted according to the output strategy.
+   */
+  public static function renderFromHtml($string);
+
+}