This package includes sources for attributes which are defined in newer .NET versions (>= .NET Core 3.0) such as
attributes required for nullable reference types, attributes required for the required keyword and others.
Just install the NuGet package and the sources will be included in your project.
If you are using the Polyfill or Nullable package these attributes are automatically disabled.
You can control inclusion of the attributes with the following MSBuild properties:
AppCoreNetAttributesEnabledEnables/disables all attributes.AppCoreNetNullableAttributesEnabledEnables/disables the nullable attributes.AppCoreNetTrimmingAttributesEnabledEnables/disables the trimming attributes.
Example:
<Project>
<PropertyGroup>
<AppCoreNetAttributesEnabled>false</AppCoreNetAttributesEnabled>
</PropertyGroup>
</Project>
This will disable all attributes.