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

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

@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Render\MarkupInterface.
+ */
+
+namespace Drupal\Component\Render;
+
+/**
+ * Marks an object's __toString() method as returning markup.
+ *
+ * Objects that implement this interface will not be automatically XSS filtered
+ * by the render system or automatically escaped by the theme engine.
+ *
+ * If there is any risk of the object's __toString() method returning
+ * user-entered data that has not been filtered first, it must not be used. If
+ * the object that implements this does not perform automatic escaping or
+ * filtering itself, then it must be marked as "@internal". For example, Views
+ * has the internal ViewsRenderPipelineMarkup object to provide a custom render
+ * pipeline in order to render JSON and to fast render fields. By contrast,
+ * FormattableMarkup and TranslatableMarkup always sanitize their output when
+ * used correctly.
+ *
+ * If the object is going to be used directly in Twig templates it should
+ * implement \Countable so it can be used in if statements.
+ *
+ * @see \Drupal\Component\Render\MarkupTrait
+ * @see \Drupal\Component\Utility\SafeMarkup::isSafe()
+ * @see \Drupal\Core\Template\TwigExtension::escapeFilter()
+ * @see \Drupal\Component\Render\FormattableMarkup
+ * @see \Drupal\Core\StringTranslation\TranslatableMarkup
+ * @see \Drupal\views\Render\ViewsRenderPipelineMarkup
+ * @see twig_render_template()
+ * @see sanitization
+ * @see theme_render
+ */
+interface MarkupInterface extends \JsonSerializable {
+
+  /**
+   * Returns markup.
+   *
+   * @return string
+   *   The markup.
+   */
+  public function __toString();
+
+}