Fixed check for RFC-1918 space.

win_domain.yaml

@@ -12,8 +12,8 @@ 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})"
-         description: Subnet must be an RFC-compliant private subnet
+      -  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: