Regex country check for custom fields

[qjul]

We've got a domain registration module for the Swedish .SE TLD. It requires that all registrants supply a personal / company ID number. So we've added a custom field for this. So far so good.

 

The crux is, that the format can be different depending on where the registrant is based. For anyone in Sweden, it has to be ten digits, no spaces or anything else. For Sweden, it seems I could add something like:

 

/^[0-9]{10}$/i

 

The problem is, I just want to require this 10 digit code for Swedish registrants, anyone else can put a more freeform ID in there.

 

I need to check this when creating a new account, as it'll be used to auto-process the domain registration and it'll fail if the ID is incorrect.