Is there a built-in IsLowerCase() in .NET?

public static bool IsLowerCase( this string text ) {
    if ( string.IsNullOrEmpty( text ) ) { return true; }
    foreach ( char c in text )
    	if ( char.IsLetter( c ) && !char.IsLower( c ) )
    		return false;

    return true;
}


"someString".IsLowerCase();

char.IsLower(c);

string upper = "CONVERTED FROM UPPERCASE";
 Console.WriteLine(upper.ToLower());

CultureInfo cultureInfo   = Thread.CurrentThread.CurrentCulture;
TextInfo textInfo = cultureInfo.TextInfo;

Console.WriteLine(textInfo.ToTitleCase(title));
Console.WriteLine(textInfo.ToLower(title));
Console.WriteLine(textInfo.ToUpper(title));

string s = ...
s.All(c => char.IsLower(c));

s.ToLower(CultureInfo.CurrentUICulture) == s;

Imports System.Runtime.CompilerServices
Module CustomExtensions

    <Extension()> _
    Public Function IsLowerCase(ByVal Input As String) As Boolean
        Return Return Input.All(Function(c) Char.IsLower(c))
    End Function

End Module

using System.Runtime.CompilerServices;
static class CustomExtensions
{
    public static bool IsLowerCase(this string Input)
    {
        return Input.All(c => char.IsLower(c));
    }
}

Console.WriteLine("ThisIsMyTestString".IsLowerCase())

public bool IsLower(string TestString)
    {
        if (String.IsNullOrEmpty(TestString))
        {
            return true;
        }

        string testlower = TestString.ToLowerInvariant();

        if (String.Compare(TestString, testlower, false) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }


    }

return Input.ToList().Exists(c => Char.IsUpper(c));

char.IsLetter( c )