Need to double escape '\' in regex

win_domain.yaml

@@ -18,7 +18,7 @@ parameters:
     constraints:
       -  length: { min: 6, max: 11 }
          description: Subnet prefix must be between 6 and 11 characters
-      -  allowed_pattern: "(192\.168\.[0-9]{1,3})|(10(\.[0-9]{1,3}){2})|(172\.(1[6-9]|2[0-9]|3[1-2])\.[0-9]{1,3})"
+      -  allowed_pattern: "(192\\.168\\.[0-9]{1,3})|(10(\\.[0-9]{1,3}){2})|(172\\.(1[6-9]|2[0-9]|3[1-2])\\.[0-9]{1,3})"
          description: Subnet must be the three-octet prefix for an RFC1918 subnet.
 
 resources: