diff --git a/core/lib/Drupal/Component/Utility/Html.php b/core/lib/Drupal/Component/Utility/Html.php
index 4dd9d27..60b83df 100644
--- a/core/lib/Drupal/Component/Utility/Html.php
+++ b/core/lib/Drupal/Component/Utility/Html.php
@@ -359,4 +359,21 @@ public static function escapeCdataElement(\DOMNode $node, $comment_start = '//',
     }
   }
 
+  /**
+   * Decodes all HTML entities including numerical ones to regular UTF-8 bytes.
+   *
+   * Double-escaped entities will only be decoded once ("<" becomes
+   * "&lt;", not "<"). Be careful when using this function, as it will revert
+   * previous sanitization efforts (&lt;script&gt; will become <script>).
+   *
+   * @param string $text
+   *   The text to decode entities in.
+   *
+   * @return string
+   *   The input $text, with all HTML entities decoded once.
+   */
+  public static function decodeEntities($text) {
+    return html_entity_decode($text, ENT_QUOTES, 'UTF-8');
+  }
+
 }
diff --git a/core/lib/Drupal/Component/Utility/SafeMarkup.php b/core/lib/Drupal/Component/Utility/SafeMarkup.php
index 56bd518..8d4cb34 100644
--- a/core/lib/Drupal/Component/Utility/SafeMarkup.php
+++ b/core/lib/Drupal/Component/Utility/SafeMarkup.php
@@ -165,4 +165,121 @@ public static function getAll() {
     return static::$safeStrings;
   }
 
+  /**
+   * Encodes special characters in a plain-text string for display as HTML.
+   *
+   * Also validates strings as UTF-8. All processed strings are also
+   * automatically flagged as safe markup strings for rendering.
+   *
+   * @param string $text
+   *   The text to be checked or processed.
+   *
+   * @return string
+   *   An HTML safe version of $text, or an empty string if $text is not
+   *   valid UTF-8.
+   *
+   * @ingroup sanitization
+   *
+   * @see drupal_validate_utf8()
+   */
+  public static function checkPlain($text) {
+    $string = htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+    static::$safeStrings[$string]['html'] = TRUE;
+    return $string;
+  }
+
+  /**
+   * Formats a string for HTML display by replacing variable placeholders.
+   *
+   * This function replaces variable placeholders in a string with the requested
+   * values and escapes the values so they can be safely displayed as HTML. It
+   * should be used on any unknown text that is intended to be printed to an
+   * HTML page (especially text that may have come from untrusted users, since
+   * in that case it prevents cross-site scripting and other security problems).
+   *
+   * In most cases, you should use t() rather than calling this function
+   * directly, since it will translate the text (on non-English-only sites) in
+   * addition to formatting it.
+   *
+   * @param $string
+   *   A string containing placeholders. The string itself is not escaped, any
+   *   unsafe content must be in $args and inserted via placeholders.
+   * @param $args
+   *   An associative array of replacements to make. Occurrences in $string of
+   *   any key in $args are replaced with the corresponding value, after
+   *   optional sanitization and formatting. The type of sanitization and
+   *   formatting depends on the first character of the key:
+   *   - @variable: Escaped to HTML using self::escape(). Use this as the
+   *     default choice for anything displayed on a page on the site.
+   *   - %variable: Escaped to HTML and formatted using self::placeholder(),
+   *     which makes the following HTML code:
+   *     @code
+   *       <em class="placeholder">text output here.</em>
+   *     @endcode
+   *   - !variable: Inserted as is, with no sanitization or formatting. Only
+   *     use this when the resulting string is being generated for one of:
+   *     - Non-HTML usage, such as a plain-text email.
+   *     - Non-direct HTML output, such as a plain-text variable that will be
+   *       printed as an HTML attribute value and therefore formatted with
+   *       self::checkPlain() as part of that.
+   *     - Some other special reason for suppressing sanitization.
+   *
+   * @return string
+   *   The formatted string, which is marked as safe unless sanitization of an
+   *   unsafe argument was suppressed (see above).
+   *
+   * @ingroup sanitization
+   *
+   * @see t()
+   */
+  public static function format($string, array $args = array()) {
+    $safe = TRUE;
+
+    // Transform arguments before inserting them.
+    foreach ($args as $key => $value) {
+      switch ($key[0]) {
+        case '@':
+          // Escaped only.
+          $args[$key] = static::escape($value);
+          break;
+
+        case '%':
+        default:
+          // Escaped and placeholder.
+          $args[$key] = static::placeholder($value);
+          break;
+
+        case '!':
+          // Pass-through.
+          if (!static::isSafe($value)) {
+            $safe = FALSE;
+          }
+      }
+    }
+
+    $output = strtr($string, $args);
+    if ($safe) {
+      static::$safeStrings[$output]['html'] = TRUE;
+    }
+
+    return $output;
+  }
+
+  /**
+   * Formats text for emphasized display in a placeholder inside a sentence.
+   *
+   * Used automatically by self::format().
+   *
+   * @param string $text
+   *   The text to format (plain-text).
+   *
+   * @return string
+   *   The formatted text (html).
+   */
+  public static function placeholder($text) {
+    $string = '<em class="placeholder">' . static::escape($text) . '</em>';
+    static::$safeStrings[$string]['html'] = TRUE;
+    return $string;
+  }
+
 }
diff --git a/core/lib/Drupal/Component/Utility/String.php b/core/lib/Drupal/Component/Utility/String.php
index b39ca5d..621043c 100644
--- a/core/lib/Drupal/Component/Utility/String.php
+++ b/core/lib/Drupal/Component/Utility/String.php
@@ -17,9 +17,6 @@ class String {
   /**
    * Encodes special characters in a plain-text string for display as HTML.
    *
-   * Also validates strings as UTF-8. All processed strings are also
-   * automatically flagged as safe markup strings for rendering.
-   *
    * @param string $text
    *   The text to be checked or processed.
    *
@@ -27,45 +24,32 @@ class String {
    *   An HTML safe version of $text, or an empty string if $text is not
    *   valid UTF-8.
    *
-   * @ingroup sanitization
-   *
-   * @see drupal_validate_utf8()
-   * @see \Drupal\Component\Utility\SafeMarkup
+   * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
+   *   Use \Drupal\Component\Utility\SafeMarkup::checkPlain() instead.
    */
   public static function checkPlain($text) {
-    return SafeMarkup::set(htmlspecialchars($text, ENT_QUOTES, 'UTF-8'));
+    return SafeMarkup::checkPlain($text);
   }
 
   /**
    * Decodes all HTML entities including numerical ones to regular UTF-8 bytes.
    *
-   * Double-escaped entities will only be decoded once ("&amp;lt;" becomes
-   * "&lt;", not "<"). Be careful when using this function, as it will revert
-   * previous sanitization efforts (&lt;script&gt; will become <script>).
-   *
    * @param string $text
    *   The text to decode entities in.
    *
    * @return string
    *   The input $text, with all HTML entities decoded once.
+   *
+   * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
+   *   Use \qDrupal\Component\Utility\Html::decodeEntities() instead.
    */
   public static function decodeEntities($text) {
-    return html_entity_decode($text, ENT_QUOTES, 'UTF-8');
+    return Html::decodeEntities($text);
   }
 
   /**
    * Formats a string for HTML display by replacing variable placeholders.
    *
-   * This function replaces variable placeholders in a string with the requested
-   * values and escapes the values so they can be safely displayed as HTML. It
-   * should be used on any unknown text that is intended to be printed to an
-   * HTML page (especially text that may have come from untrusted users, since
-   * in that case it prevents cross-site scripting and other security problems).
-   *
-   * In most cases, you should use t() rather than calling this function
-   * directly, since it will translate the text (on non-English-only sites) in
-   * addition to formatting it.
-   *
    * @param $string
    *   A string containing placeholders. The string itself is not escaped, any
    *   unsafe content must be in $args and inserted via placeholders.
@@ -94,57 +78,27 @@ public static function decodeEntities($text) {
    *   The formatted string, which is marked as safe unless sanitization of an
    *   unsafe argument was suppressed (see above).
    *
-   * @ingroup sanitization
-   *
-   * @see t()
+   * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
+   *   Use \Drupal\Component\Utility\SafeMarkup::format() instead.
    */
   public static function format($string, array $args = array()) {
-    $safe = TRUE;
-
-    // Transform arguments before inserting them.
-    foreach ($args as $key => $value) {
-      switch ($key[0]) {
-        case '@':
-          // Escaped only.
-          $args[$key] = SafeMarkup::escape($value);
-          break;
-
-        case '%':
-        default:
-          // Escaped and placeholder.
-          $args[$key] = static::placeholder($value);
-          break;
-
-        case '!':
-          // Pass-through.
-          if (!SafeMarkup::isSafe($value)) {
-            $safe = FALSE;
-          }
-      }
-    }
-
-    $output = strtr($string, $args);
-    if ($safe) {
-      SafeMarkup::set($output);
-    }
-
-    return $output;
+    return SafeMarkup::format($string, $args);
   }
 
   /**
    * Formats text for emphasized display in a placeholder inside a sentence.
    *
-   * Used automatically by self::format().
-   *
    * @param string $text
    *   The text to format (plain-text).
    *
    * @return string
    *   The formatted text (html).
+   *
+   * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
+   *   Use \Drupal\Component\Utility\SafeMarkup::placeholder() instead.
    */
   public static function placeholder($text) {
-    return SafeMarkup::set('<em class="placeholder">' . SafeMarkup::escape($text) . '</em>');
+    return SafeMarkup::placeholder($text);
   }
 
-
 }