diff --git a/core/lib/Drupal/Component/Utility/Unicode.php b/core/lib/Drupal/Component/Utility/Unicode.php
index 0ca1c2a..f092d11 100644
--- a/core/lib/Drupal/Component/Utility/Unicode.php
+++ b/core/lib/Drupal/Component/Utility/Unicode.php
@@ -607,6 +607,7 @@ public static function strcasecmp($str1 , $str2) {
    */
   public static function mimeHeaderEncode($string) {
     if (preg_match('/[^\x20-\x7E]/', $string)) {
+      // Chunk size: floor((75 - strlen("=?UTF-8?B??=")) * 0.75); .
       $chunk_size = 47;
       $len = strlen($string);
       $output = '';