/Drupal 8

protected static function FormattableMarkup::placeholderFormat

protected static FormattableMarkup::placeholderFormat($string, array $args)

Replaces placeholders in a string with values.


string $string: A string containing placeholders. The string itself is expected to be safe and correct HTML. Any unsafe content must be in $args and inserted via placeholders.

array $args: An associative array of replacements. Each array key should be the same as a placeholder in $string. The corresponding value should be a string or an object that implements \Drupal\Component\Render\MarkupInterface. The value replaces the placeholder in $string. Sanitization and formatting will be done before replacement. The type of sanitization and formatting depends on the first character of the key:

        $this->placeholderFormat('This will force HTML-escaping of the replacement value: @text', ['@text' => (string) $safe_string_interface_object));

Use this placeholder as the default choice for anything displayed on the site, but not within HTML attributes, JavaScript, or CSS. Doing so is a security risk.

  • %variable: Use when the replacement value is to be wrapped in <em> tags. A call like:
      $string = "%output_text";
      $arguments = ['output_text' => 'text output here.'];
      $this->placeholderFormat($string, $arguments);

makes the following HTML code:

      <em class="placeholder">text output here.em>

As with @variable, do not use this within HTML attributes, JavaScript, or CSS. Doing so is a security risk.

    // Secure (with quotes):
    $this->placeholderFormat('<a href=":url">@variable</a>', [':url' => $url, '@variable' => $variable]);
    // Insecure (without quotes):
    $this->placeholderFormat('<a href=:url>@variable</a>', [':url' => $url, '@variable' => $variable]);

When ":variable" comes from arbitrary user input, the result is secure, but not guaranteed to be a valid URL (which means the resulting output could fail HTML validation). To guarantee a valid URL, use Url::fromUri($user_input)->toString() (which either throws an exception or returns a well-formed URL) before passing the result into a ":variable" placeholder.

Return value

string A formatted HTML string with the placeholders replaced.

See also






Related topics

Sanitization functions
Functions to sanitize values.


core/lib/Drupal/Component/Render/FormattableMarkup.php, line 188


Formats a string for HTML display by replacing variable placeholders.




protected static function placeholderFormat($string, array $args) {
  // Transform arguments before inserting them.
  foreach ($args as $key => $value) {
    switch ($key[0]) {
      case '@':
        // Escape if the value is not an object from a class that implements
        // \Drupal\Component\Render\MarkupInterface, for example strings will
        // be escaped.
        // Strings that are safe within HTML fragments, but not within other
        // contexts, may still be an instance of
        // \Drupal\Component\Render\MarkupInterface, so this placeholder type
        // must not be used within HTML attributes, JavaScript, or CSS.
        $args[$key] = static::placeholderEscape($value);

      case ':':
        // Strip URL protocols that can be XSS vectors.
        $value = UrlHelper::stripDangerousProtocols($value);
        // Escape unconditionally, without checking whether the value is an
        // instance of \Drupal\Component\Render\MarkupInterface. This forces
        // characters that are unsafe for use in an "href" HTML attribute to
        // be encoded. If a caller wants to pass a value that is extracted
        // from HTML and therefore is already HTML encoded, it must invoke
        // \Drupal\Component\Render\OutputStrategyInterface::renderFromHtml()
        // on it prior to passing it in as a placeholder value of this type.
        // @todo Add some advice and stronger warnings.
        //   https://www.drupal.org/node/2569041.
        $args[$key] = Html::escape($value);

      case '%':
        // Similarly to @, escape non-safe values. Also, add wrapping markup
        // in order to render as a placeholder. Not for use within attributes,
        // per the warning above about
        // \Drupal\Component\Render\MarkupInterface and also due to the
        // wrapping markup.
        $args[$key] = '<em class="placeholder">' . static::placeholderEscape($value) . '</em>';

        // We do not trigger an error for placeholder that start with an
        // alphabetic character.
        if (!ctype_alpha($key[0])) {
          // We trigger an error as we may want to introduce new placeholders
          // in the future without breaking backward compatibility.
          trigger_error('Invalid placeholder (' . $key . ') in string: ' . $string, E_USER_ERROR);

  return strtr($string, $args);

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