code: public static function stripPrefix($s, $prefix, $caseInsensitive = false)
      {
          // substr_compare errors if $main_str is zero-length, so handle that
          // case specially here.
          if (strlen($s) == 0) {
              if (strlen($prefix) == 0) {
                  return $s;
              } else {
                  return null;
              }
          }
  
          $prefix_length = strlen($prefix);
          if (\substr_compare($s, $prefix, 0, strlen($prefix), $caseInsensitive) == 0) {
              return substr($s, $prefix_length);
          }
      }
docs: If `$s` starts with `$prefix`, return `$s` with `$prefix` removed.  Otherwise,
  return `null`.
  
  @param string $s
  @param string $prefix
  @param bool $caseInsensitive
  
  @return string|null