docs: add regex101.com links.

Author: ytetsuro

system/Validation/FormatRules.php

@@ -44,6 +44,7 @@ public function alpha_space(?string $value = null): bool
 			return true;
 		}
 
+		// @see https://regex101.com/r/LhqHPO/1
 		return (bool) preg_match('/\A[A-Z ]+\z/i', $value);
 	}
 
@@ -56,7 +57,8 @@ public function alpha_space(?string $value = null): bool
 	 */
 	public function alpha_dash(?string $str = null): bool
 	{
-			return (bool) preg_match('/\A[a-z0-9_-]+\z/i', $str);
+		// @see https://regex101.com/r/XfVY3d/1
+		return (bool) preg_match('/\A[a-z0-9_-]+\z/i', $str);
 	}
 
 	/**
@@ -72,6 +74,7 @@ public function alpha_dash(?string $str = null): bool
 	 */
 	public function alpha_numeric_punct($str)
 	{
+		// @see https://regex101.com/r/6N8dDY/1
 		return (bool) preg_match('/\A[A-Z0-9 ~!#$%\&\*\-_+=|:.]+\z/i', $str);
 	}
 
@@ -96,6 +99,7 @@ public function alpha_numeric(?string $str = null): bool
 	 */
 	public function alpha_numeric_space(?string $str = null): bool
 	{
+		// @see https://regex101.com/r/0AZDME/1
 		return (bool) preg_match('/\A[A-Z0-9 ]+\z/i', $str);
 	}
 
@@ -123,6 +127,7 @@ public function string($str = null): bool
 	 */
 	public function decimal(?string $str = null): bool
 	{
+		// @see https://regex101.com/r/HULifl/1/
 		return (bool) preg_match('/\A[-+]?[0-9]{0,}\.?[0-9]+\z/', $str);
 	}
 
@@ -181,6 +186,7 @@ public function is_natural_no_zero(?string $str = null): bool
 	 */
 	public function numeric(?string $str = null): bool
 	{
+		// @see https://regex101.com/r/bb9wtr/1
 		return (bool) preg_match('/\A[\-+]?[0-9]*\.?[0-9]+\z/', $str);
 	}
 
@@ -253,6 +259,7 @@ public function valid_json(string $str = null): bool
 	 */
 	public function valid_email(string $str = null): bool
 	{
+		// @see https://regex101.com/r/wlJG1t/1/
 		if (function_exists('idn_to_ascii') && defined('INTL_IDNA_VARIANT_UTS46') && preg_match('#\A([^@]+)@(.+)\z#', $str, $matches))
 		{
 			$str = $matches[1] . '@' . idn_to_ascii($matches[2], 0, INTL_IDNA_VARIANT_UTS46);