system/Validation/FormatRules.php
public function regex_match(string $str = null, string $pattern, array $data): bool
	{
		if (strpos($pattern, '/') !== 0)
		{
			$pattern = "/{$pattern}/";
		}

		return (bool) preg_match($pattern, $str);
	}
public function regex_match(string $str = null, string $pattern, array $data): bool
	{
		if (strpos($pattern, '/') !== 0)
		{
			$pattern = "/{$pattern}/";
		}

		return (bool) preg_match($pattern, $str);
	}
Compares value against a regular expression pattern.

@param string $str
@param string $pattern
@param array  $data    Other field/value pairs

@return boolean