title: NuGet package for FlowDocument .NET Core 3
body: <p>According to <a href="https://docs.microsoft.com/en-us/dotnet/api/system.windows.documents.flowdocument?view=netframework-4.8" rel="nofollow noreferrer">this MS page</a> <code>FlowDocument</code> is part of .NET Core 3.0 under the Namespace:
  <code>System.Windows.Documents</code>.  However, I cannot find <code>System.Windows.Documents</code> NuGet package, so what is the correct NuGet package?</p>
  
  <p>Sorry for the simple questions but my searching has returned nothing.</p>
  
  <p>Thanks!</p>
  
  <p>edit:  Yes I have "Include prerelease" checked.</p>