diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index e1c15fe..9cc6615 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2,6 +2,7 @@
 
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Component\Utility\Settings;
+use Drupal\Component\Utility\String;
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Database\Database;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
@@ -1554,75 +1555,23 @@ function t($string, array $args = array(), array $options = array()) {
 /**
  * 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.
- * @param $args
- *   An associative array of replacements to make. Occurrences in $string of
- *   any key in $args are replaced with the corresponding value, after optional
- *   sanitization and formatting. The type of sanitization and formatting
- *   depends on the first character of the key:
- *   - @variable: Escaped to HTML using check_plain(). Use this as the default
- *     choice for anything displayed on a page on the site.
- *   - %variable: Escaped to HTML and formatted using drupal_placeholder(),
- *     which makes it display as <em>emphasized</em> text.
- *   - !variable: Inserted as is, with no sanitization or formatting. Only use
- *     this for text that has already been prepared for HTML display (for
- *     example, user-supplied text that has already been run through
- *     check_plain() previously, or is expected to contain some limited HTML
- *     tags and has already been run through filter_xss() previously).
- *
+ * @see \Drupal\Component\Utility\String::format()
  * @see t()
  * @ingroup sanitization
  */
 function format_string($string, array $args = array()) {
-  // Transform arguments before inserting them.
-  foreach ($args as $key => $value) {
-    switch ($key[0]) {
-      case '@':
-        // Escaped only.
-        $args[$key] = check_plain($value);
-        break;
-
-      case '%':
-      default:
-        // Escaped and placeholder.
-        $args[$key] = drupal_placeholder($value);
-        break;
-
-      case '!':
-        // Pass-through.
-    }
-  }
-  return strtr($string, $args);
+  return String::format($string, $args);
 }
 
 /**
  * Encodes special characters in a plain-text string for display as HTML.
  *
- * Also validates strings as UTF-8.
- *
- * @param $text
- *   The text to be checked or processed.
- *
- * @return
- *   An HTML safe version of $text, or an empty string if $text is not
- *   valid UTF-8.
- *
+ * @see \Drupal\Component\Utility\String::checkPlain()
  * @see drupal_validate_utf8()
  * @ingroup sanitization
  */
 function check_plain($text) {
-  return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+  return String::checkPlain($text);
 }
 
 /**
@@ -3381,16 +3330,10 @@ function drupal_is_cli() {
 /**
  * Formats text for emphasized display in a placeholder inside a sentence.
  *
- * Used automatically by format_string().
- *
- * @param $text
- *   The text to format (plain-text).
- *
- * @return
- *   The formatted text (html).
+ * @see \Drupal\Component\Utility\String::placeholder()
  */
 function drupal_placeholder($text) {
-  return '<em class="placeholder">' . check_plain($text) . '</em>';
+  return String::placeholder($text);
 }
 
 /**
diff --git a/core/lib/Drupal/Component/Utility/String.php b/core/lib/Drupal/Component/Utility/String.php
new file mode 100644
index 0000000..c79b5af
--- /dev/null
+++ b/core/lib/Drupal/Component/Utility/String.php
@@ -0,0 +1,108 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Utility\String.
+ */
+
+namespace Drupal\Component\Utility;
+
+/**
+ * Provides helpers to operate on strings.
+ */
+class String {
+
+  /**
+   * Encodes special characters in a plain-text string for display as HTML.
+   *
+   * Also validates strings as UTF-8.
+   *
+   * @param string $text
+   *   The text to be checked or processed.
+   *
+   * @return string
+   *   An HTML safe version of $text, or an empty string if $text is not
+   *   valid UTF-8.
+   *
+   * @see drupal_validate_utf8()
+   * @ingroup sanitization
+   */
+  public static function checkPlain($text) {
+    return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+  }
+
+  /**
+   * 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.
+   * @param $args
+   *   An associative array of replacements to make. Occurrences in $string of
+   *   any key in $args are replaced with the corresponding value, after optional
+   *   sanitization and formatting. The type of sanitization and formatting
+   *   depends on the first character of the key:
+   *   - @variable: Escaped to HTML using String::checkPlain(). Use this as the
+   *     default choice for anything displayed on a page on the site.
+   *   - %variable: Escaped to HTML and formatted using String::placeholder(),
+   *     which makes it display as <em>emphasized</em> text.
+   *   - !variable: Inserted as is, with no sanitization or formatting. Only use
+   *     this for text that has already been prepared for HTML display (for
+   *     example, user-supplied text that has already been run through
+   *     String::checkPlain() previously, or is expected to contain some limited
+   *     HTML tags and has already been run through filter_xss() previously).
+   *
+   *
+   * @see t()
+   * @ingroup sanitization
+   *
+   * @return mixte
+   *  The formatted string with placeholders inserted, or FALSE if no args specified.
+   */
+  public static function format($string, array $args = array()) {
+    // Transform arguments before inserting them.
+    foreach ($args as $key => $value) {
+      switch ($key[0]) {
+        case '@':
+          // Escaped only.
+          $args[$key] = static::checkPlain($value);
+          break;
+
+        case '%':
+        default:
+          // Escaped and placeholder.
+          $args[$key] = static::placeholder($value);
+          break;
+
+        case '!':
+          // Pass-through.
+      }
+    }
+    return strtr($string, $args);
+  }
+
+  /**
+   * Formats text for emphasized display in a placeholder inside a sentence.
+   *
+   * Used automatically by self::format().
+   *
+   * @param string $text
+   *   The text to format (plain-text).
+   *
+   * @return string
+   *   The formatted text (html).
+   */
+  public static function placeholder($text) {
+    return '<em class="placeholder">' . static::checkPlain($text) . '</em>';
+  }
+
+}
diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/XssUnitTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/XssUnitTest.php
index dff85bd..57863ff 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/XssUnitTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/XssUnitTest.php
@@ -10,7 +10,7 @@
 use Drupal\simpletest\DrupalUnitTestBase;
 
 /**
- * Tests for check_plain(), filter_xss(), format_string(), and check_url().
+ * Tests for filter_xss() and check_url().
  */
 class XssUnitTest extends DrupalUnitTestBase {
 
@@ -24,7 +24,7 @@ class XssUnitTest extends DrupalUnitTestBase {
   public static function getInfo() {
     return array(
       'name' => 'String filtering tests',
-      'description' => 'Confirm that check_plain(), filter_xss(), format_string() and check_url() work correctly, including invalid multi-byte sequences.',
+      'description' => 'Confirm that filter_xss() and check_url() work correctly, including invalid multi-byte sequences.',
       'group' => 'Common',
     );
   }
@@ -38,14 +38,6 @@ protected function setUp() {
    * Checks that invalid multi-byte sequences are rejected.
    */
   function testInvalidMultiByte() {
-     // Ignore PHP 5.3+ invalid multibyte sequence warning.
-     $text = @check_plain("Foo\xC0barbaz");
-     $this->assertEqual($text, '', 'check_plain() rejects invalid sequence "Foo\xC0barbaz"');
-     // Ignore PHP 5.3+ invalid multibyte sequence warning.
-     $text = @check_plain("\xc2\"");
-     $this->assertEqual($text, '', 'check_plain() rejects invalid sequence "\xc2\""');
-     $text = check_plain("Fooÿñ");
-     $this->assertEqual($text, "Fooÿñ", 'check_plain() accepts valid sequence "Fooÿñ"');
      $text = filter_xss("Foo\xC0barbaz");
      $this->assertEqual($text, '', 'filter_xss() rejects invalid sequence "Foo\xC0barbaz"');
      $text = filter_xss("Fooÿñ");
@@ -53,29 +45,17 @@ function testInvalidMultiByte() {
   }
 
   /**
-   * Checks that special characters are escaped.
+   * Tests t() functionality.
    */
-  function testEscaping() {
-     $text = check_plain("<script>");
-     $this->assertEqual($text, '&lt;script&gt;', 'check_plain() escapes &lt;script&gt;');
-     $text = check_plain('<>&"\'');
-     $this->assertEqual($text, '&lt;&gt;&amp;&quot;&#039;', 'check_plain() escapes reserved HTML characters.');
-  }
-
-  /**
-   * Tests t() and format_string() replacement functionality.
-   */
-  function testFormatStringAndT() {
-    foreach (array('format_string', 't') as $function) {
-      $text = $function('Simple text');
-      $this->assertEqual($text, 'Simple text', $function . ' leaves simple text alone.');
-      $text = $function('Escaped text: @value', array('@value' => '<script>'));
-      $this->assertEqual($text, 'Escaped text: &lt;script&gt;', $function . ' replaces and escapes string.');
-      $text = $function('Placeholder text: %value', array('%value' => '<script>'));
-      $this->assertEqual($text, 'Placeholder text: <em class="placeholder">&lt;script&gt;</em>', $function . ' replaces, escapes and themes string.');
-      $text = $function('Verbatim text: !value', array('!value' => '<script>'));
-      $this->assertEqual($text, 'Verbatim text: <script>', $function . ' replaces verbatim string as-is.');
-    }
+  function testT() {
+    $text = t('Simple text');
+    $this->assertEqual($text, 'Simple text', 't leaves simple text alone.');
+    $text = t('Escaped text: @value', array('@value' => '<script>'));
+    $this->assertEqual($text, 'Escaped text: &lt;script&gt;', 't replaces and escapes string.');
+    $text = t('Placeholder text: %value', array('%value' => '<script>'));
+    $this->assertEqual($text, 'Placeholder text: <em class="placeholder">&lt;script&gt;</em>', 't replaces, escapes and themes string.');
+    $text = t('Verbatim text: !value', array('!value' => '<script>'));
+    $this->assertEqual($text, 'Verbatim text: <script>', 't replaces verbatim string as-is.');
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Component/Utility/StringTest.php b/core/tests/Drupal/Tests/Component/Utility/StringTest.php
new file mode 100644
index 0000000..4bac498
--- /dev/null
+++ b/core/tests/Drupal/Tests/Component/Utility/StringTest.php
@@ -0,0 +1,109 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Component\Utillity\StringTest.
+ */
+
+namespace Drupal\Tests\Component\Utility;
+
+use Drupal\Tests\UnitTestCase;
+use Drupal\Component\Utility\String;
+
+/**
+ * Tests string filtering.
+ *
+ * @see \Drupal\Component\Utility\String
+ */
+class StringTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'String filtering tests',
+      'description' => 'Confirm that String::checkPlain() and String::format() work correctly, including invalid multi-byte sequences.',
+      'group' => 'Common',
+    );
+  }
+
+  /**
+   * Tests String::checkPlain().
+   *
+   * @dataProvider providerCheckPlain
+   *
+   * @param string $text
+   *   The text to provide to String::checkPlain().
+   * @param string $expected
+   *   The expected output from the function.
+   * @param string $message
+   *   The message to provide as output for the test.
+   * @param bool $ignorewarnings
+   *   Whether or not to ignore PHP 5.3+ invalid multibyte sequence warnings.
+   */
+  function testCheckPlain($text, $expected, $message, $ignorewarnings = FALSE) {
+    $result = $ignorewarnings ? @String::checkPlain($text) : String::checkPlain($text);
+    $this->assertEquals($result, $expected, $message);
+  }
+
+  /**
+   * Data provider for testCheckPlain().
+   *
+   * @see testCheckPlain()
+   */
+  function providerCheckPlain() {
+    // Checks that invalid multi-byte sequences are rejected.
+    $tests[] = array("Foo\xC0barbaz", '', 'String::checkPlain() rejects invalid sequence "Foo\xC0barbaz"', TRUE);
+    $tests[] = array("\xc2\"", '', 'String::checkPlain() rejects invalid sequence "\xc2\""', TRUE);
+    $tests[] = array("Fooÿñ", "Fooÿñ", 'String::checkPlain() accepts valid sequence "Fooÿñ"');
+
+    // Checks that special characters are escaped.
+    $tests[] = array("<script>", '&lt;script&gt;', 'String::checkPlain() escapes &lt;script&gt;');
+    $tests[] = array('<>&"\'', '&lt;&gt;&amp;&quot;&#039;', 'String::checkPlain() escapes reserved HTML characters.');
+
+    return $tests;
+  }
+
+  /**
+   * Tests string formatting with String::format().
+   *
+   * @dataProvider providerFormat
+   *
+   * @param string $string
+   *   The string to run through String::format().
+   * @param string $args
+   *   The arguments to pass into String::format().
+   * @param string $expected
+   *   The expected result from calling the function.
+   * @param string $message
+   *   The message to display as output to the test.
+   *
+   * @see String::format()
+   */
+  function testFormat($string, $args, $expected, $message) {
+    $result = String::format($string, $args);
+    $this->assertEquals($result, $expected, $message);
+  }
+
+  /**
+   * Data provider for testFormat().
+   *
+   * @see testFormat()
+   */
+  function providerFormat() {
+    $tests[] = array('Simple text', array(), 'Simple text', 'String::format leaves simple text alone.');
+    $tests[] = array('Escaped text: @value', array('@value' => '<script>'), 'Escaped text: &lt;script&gt;', 'String::format replaces and escapes string.');
+    $tests[] = array('Placeholder text: %value', array('%value' => '<script>'), 'Placeholder text: <em class="placeholder">&lt;script&gt;</em>', 'String::format replaces, escapes and themes string.');
+    $tests[] = array('Verbatim text: !value', array('!value' => '<script>'), 'Verbatim text: <script>', 'String::format replaces verbatim string as-is.');
+
+    return $tests;
+  }
+
+  /**
+   * Tests String::placeholder().
+   *
+   * @see String::placeholder()
+   */
+  function testPlaceholder() {
+    $this->assertEquals('<em class="placeholder">Some text</em>', String::placeholder('Some text'));
+  }
+
+}