<PackageReference Include="System.Configuration.ConfigurationManager" Version="9.0.3" />

RegexStringValidatorAttribute

Declaratively instructs .NET to perform string validation on a configuration property using a regular expression. This class cannot be inherited.
namespace System.Configuration { [AttributeUsage(AttributeTargets.Property)] public sealed class RegexStringValidatorAttribute : ConfigurationValidatorAttribute { public override ConfigurationValidatorBase ValidatorInstance => new RegexStringValidator(Regex); public string Regex { get; } public RegexStringValidatorAttribute(string regex) { Regex = regex; } } }