I've written a Regular expression which should validate a string using the following rules:

1. The first four characters must be alphanumeric.
2. The alpha characters are followed by 6 or 7 numeric values for a total length of 10 or 11.

So the string should look like this if its valid:

> 
> CCCCNNNNNN or CCCCNNNNNNN
> 
> 
> 

C being any character and N being a number.

My expression is written: `@"^[0-9A-Za-z]{3}[0-9A-Za-z-]\d{0,21}$";`

My regex match code looks like this:

```
var cc1 = "FOOBAR"; // should fail.
var cc2 = "AAAA1111111111"; // should succeed

var regex = @"^[0-9A-Za-z]{3}[0-9A-Za-z-]\d{0,21}$";

Match match = Regex.Match( cc1, regex, RegexOptions.IgnoreCase );

if ( cc1 != string.Empty && match.Success )
{
     //"The Number must start with 4 letters and contain no numbers.",
     Error = SeverityType.Error
}

```

I'm hoping someone can take a look at my expression and offer some feedback on improvements to produce a valid match.

Also, am I use `.Match()` correctly? If `Match.Success` is `true`, then does that mean that the string is valid?