document reasons for supporting framework targets (issue #68)

FRAMEWORK_SUPPORT.md

@@ -0,0 +1,33 @@
+# Framework Support
+
+This package attempts to maintain support for all versions of .NET Framework, .NET Core, Mono,
+Xamarin, and etc. that are still officially supported by their maintainers. As of v3.0.0 of the
+package, this is accomplished by multi-targeting the following targets:
+
+* .NET Standard 2.0
+* .NET Standard 2.1
+* .NET 5
+
+The reason for targeting each is given in the sections below.
+
+## .NET Standard 2.0
+
+.NET Standard 2.0 is the newest version of the .NET Standard API specification that still supports
+the .NET Framework. This is necessary to continue to support the Microsoft supported versions of
+.NET Framework (e.g. .NET Framework 4.6.1 through 4.8.X). This also includes support for
+serialization which .NET Standard 1.X did not support.
+
+## .NET Standard 2.1
+
+.NET Standard 2.1 supports C# 8.0 which includes support for nullable reference types. Including
+this target allows users of the package targeting frameworks with nullable reference types to
+benefit from type information about which references can or can't be null in the package.
+
+## .NET 5
+
+The `MemberNotNullWhenAttribute` was introduced with .NET 5. This attribute allows the package to
+provide better null handling for properties in the range types. To provide better support, the
+[Nullable](https://github.com/manuelroemer/Nullable) package is used to provide this attribute in
+earlier .NET versions. However, this adds types to the package that aren't needed in .NET 5. Thus
+publishing a .NET 5 version of the package allows for a smaller assembly and one that uses the type
+built into the framework when using .NET 5+.

Semver.Test/TestCases/NpmRangeParsingTestCase.cs

@@ -63,7 +63,6 @@ private NpmRangeParsingTestCase(
         #endregion
 
         #region Invalid Values
-
         public Type? ExceptionType { get; }
         public string? ExceptionMessageFormat { get; }
         #endregion