C# style string formatter using regex to search for key and replace with IFormattable.Format

Generic Regex Formatter.cs

using System;
using System.Linq;
using System.Text.RegularExpressions;

public static class RegexFormatter
{
	static readonly Regex FormatterPattern = new Regex(@"\{([^\{\}]+?)(?:\:([^\{\}]*))?\}",RegexOptions.Multiline);
	public static string RegexFormat(this string input,Func<string,object> selector)
	{
		return FormatterPattern.Replace(input,(match) => {
			var capture = match?.Groups?.OfType<Group>().Skip(1).Select((group) => group.Value).ToArray();
			if(!(capture?.FirstOrDefault() is string key && selector(key) is var value && value != null))
				return match.Value;

			return capture.Length > 1 && value is IFormattable formattable ? formattable.ToString(capture[1],null) : value.ToString();
		});
	}
}

Console.WriteLine("{0}".RegexFormat((key) => 100 / 3f)); // 33.33333
Console.WriteLine("{0:000.00}".RegexFormat((key) => 100 / 3f)); // 033.33