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Asked: 2026-05-10T21:24:01+00:00

I want to do preliminary check if entered string looks like Vehicle Identification Number

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I want to do preliminary check if entered string looks like Vehicle Identification Number (VIN). I know what it consists of 17 letters and digits, but letters I, O and Q are not allowed inside VIN, so I use this regular expression:

^[0-9A-Z-[IOQ]]{17}$

Now if I check a string like 1G1FP22PXS2100001 with RegularExpressionValidator it fails, but CustomValidator with this OnServerValidate event handler

Regex r = new Regex('^[0-9A-Z-[IOQ]]{17}$'); args.IsValid = r.IsMatch(TextBox1.Text);

works well.

Experiments show what RegularExpressionValidator doesn’t support Character Class Subtraction, but Regex class does.

Now I am interested why do these two .NET classes use different regex flavors? Is it documented somethere?

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1 Answer

  1. The RegularExpressionValidator also supports client-side validation using JavaScript, where the JavaScript Regex engine is used. The difference you see is the difference between the JavaScript and the .NET regex implementation. You can disable client-side validation and thus force the validator to use the .NET regex engine, at the price of the additional post-back.

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