fix(isPostalCode): Improve Dutch postal code regex

[RobinvanderVliet]

I have improved the regular expression for postal codes of the Netherlands. They cannot start with a zero, and they cannot contain "SA", "SD" and "SS".

More information: https://en.wikipedia.org/wiki/Postal_codes_in_the_Netherlands

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[WikiRik]

Is there maybe a link by PostNL (the national postal carrier) that explains these rules that we can use as a source?

[RobinvanderVliet]

Is there maybe a link by PostNL (the national postal carrier) that explains these rules that we can use as a source?

I checked their website, and I cannot find anything on there that explains it. There are plenty of other resources on the web that explain the rules.

If you search "postcodekaart" (postal code map), you will see lots of maps. You can easily notice they never start with zero.

The letter combinations "SA", "SD" and "SS" are avoided because of their associations with the Nazi occupation.

[WikiRik]

Yeah, I've seen these changes in various other maps but I was hoping for some better source. I'll try to search for them in the coming days before approving this PR, since I do think these changes are correct

[RobinvanderVliet]

I found more maps and lists, but couldn't really find a (semi-)official source unfortunately. Others suggest this regex (or similar ones) as well for Dutch postal codes

I came across an official source containing the same regular expression: https://tracking.postnl.nl/track-and-trace/api/trackAndTrace/countries

[WikiRik]

Ah nice, and I see they have different countries as well. Could you add those in a separate PR?

[RobinvanderVliet]

Ah nice, and I see they have different countries as well. Could you add those in a separate PR?

PostNL provides 20 regular expressions in total. I've compared the rest to those that we already have in validator.js, and ours are the same or more specific.

[RobinvanderVliet]

Is there anything else that needs to be done before this pull request can be merged? Let me know if there's anything I can do to help.