function FormattableMarkup::placeholderFormat

Same name and namespace in other branches
  1. 9 core/lib/Drupal/Component/Render/FormattableMarkup.php \Drupal\Component\Render\FormattableMarkup::placeholderFormat()
  2. 10 core/lib/Drupal/Component/Render/FormattableMarkup.php \Drupal\Component\Render\FormattableMarkup::placeholderFormat()
  3. 11.x core/lib/Drupal/Component/Render/FormattableMarkup.php \Drupal\Component\Render\FormattableMarkup::placeholderFormat()

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:

  • @variable: When the placeholder replacement value is:

        $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.

  • :variable: Return value is escaped with \Drupal\Component\Utility\Html::escape() and filtered for dangerous protocols using UrlHelper::stripDangerousProtocols(). Use this when using the "href" attribute, ensuring the attribute value is always wrapped in quotes:
// 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

3 calls to FormattableMarkup::placeholderFormat()
FormattableMarkup::__toString in core/lib/Drupal/Component/Render/FormattableMarkup.php
Returns markup.
PluralTranslatableMarkup::render in core/lib/Drupal/Core/StringTranslation/PluralTranslatableMarkup.php
Renders the object as a string.
TranslatableMarkup::render in core/lib/Drupal/Core/StringTranslation/TranslatableMarkup.php
Renders the object as a string.


core/lib/Drupal/Component/Render/FormattableMarkup.php, line 194


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.
                $args[$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($value) . '</em>';
                // We do not trigger an error for placeholder that start with an
                // alphabetic character.
                // @todo Change to an exception
                //   and always throw regardless of the first character.
                if (!ctype_alpha($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: ' . $string, E_USER_ERROR);
                elseif (strpos($string, $key) !== FALSE) {
                    trigger_error('Invalid placeholder (' . $key . ') in string: ' . $string, E_USER_DEPRECATED);
                // No replacement possible therefore we can discard the argument.
    return strtr($string, $args);

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