Great tip. There are at least 2 other similar use cases with leading zeros that come up in the US New England states - Zip codes and Social Security Numbers (SSN). On Cape Cod Massachusetts your postal code might be 02633. A helpful Regular Expression that covers New England zip codes that still works for Beverley Hills 90210 on the west coast of the US might look like ^\d{5}$|^\d{5}-\d{4}$.  This would allow a 5 digit zip code or the more precise "Zip+4" format. If you were issued a Social Security Number in a New England state or New York after 1973 you might have a number starting with one or 2 leading zeros such as 001-11-1111. A useful Regular Expression for SSNs might be ^\d{3}-\d{2}-\d{4}$.