system/Validation/Rules.php
public function exact_length(string $str = null, string $val, array $data): bool
	{
		$val = explode(',', $val);
		foreach ($val as $tmp)
		{
			if (is_numeric($tmp) && (int)$tmp === mb_strlen($str))
			{
				return true;
			}
		}

		return false;
	}
public function exact_length(string $str = null, string $val, array $data): bool
	{
		$val = explode(',', $val);
		foreach ($val as $tmp)
		{
			if (is_numeric($tmp) && (int)$tmp === mb_strlen($str))
			{
				return true;
			}
		}

		return false;
	}
Returns true if $str is $val characters long.
$val = "5" (one) | "5,8,12" (multiple values)

@param string $str
@param string $val
@param array  $data

@return boolean