Make error messages for disallowed values more explicit

MD_STD_IN.php

@@ -107,7 +107,7 @@ public static function get_http_input_text(string $var_name, string $default = "
         else $output = self::sanitize_text($default);
 
         if (!empty($allowed) and !\in_array($output, $allowed, true)) {
-            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: " . implode(', ', $allowed));
+            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: '" . implode('\', \'', $allowed) . "'");
         }
 
         return $output;
@@ -132,7 +132,7 @@ public static function get_http_post_text(string $var_name, string $default = ""
         else $output = self::sanitize_text($default);
 
         if (!empty($allowed) and !\in_array($output, $allowed, true)) {
-            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: " . implode(', ', $allowed));
+            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: '" . implode('\', \'', $allowed) . "'");
         }
 
         return $output;