title: NuGet PackageReference not compatible with current framework version
body: <p>I am working to move out NuGet references from using the packages.json format to PackageReferences. I have an issue with NuGet package compatibility: The package supports an older version of the .NET Framework.</p>
  
  <p>This, using the packages.json format, works just fine.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;packages&gt;
    &lt;package id="MarkdownDeep.NET-Signed" version="1.5" targetFramework="net461" /&gt;
  &lt;/packages&gt;
  
  &lt;Reference Include="MarkdownDeep, Version=1.5.5082.29984, Culture=neutral, PublicKeyToken=65640b2d9fe5ac0e, processorArchitecture=MSIL"&gt;
    &lt;HintPath&gt;..\..\packages\MarkdownDeep.NET-Signed.1.5\lib\.NetFramework 3.5\MarkdownDeep.dll&lt;/HintPath&gt;
    &lt;Private&gt;True&lt;/Private&gt;
  &lt;/Reference&gt;
  </code></pre>
  
  <p>However, replacing this with a PackageReference instruction in the .csproj file results in the error below:</p>
  
  <pre><code>&lt;PackageReference Include="MarkdownDeep.NET-Signed"&gt;
    &lt;Version&gt;1.5&lt;/Version&gt;
  &lt;/PackageReference&gt;
  </code></pre>
  
  <blockquote>
    <p>"C:\Source\WebApp.csproj" (Restore target) (1) -> (Restore target) -> 
    C:\Source\WebApp.csproj : error NU1202: Package
    MarkdownDeep.NET-Signed 1.5.0 is not compatible with net472
    (.NETFramework,Version=v4.7.2). Package MarkdownDeep.NET-Signed 1.5.0
    supports: netframework35 (.NetFramework 3.5,Version=v0.0)</p>
  </blockquote>
  
  <p>Note that the current target framework in both cases is the same, v4.7.2.</p>
  
  <p>Are there any additional instruction to add to the <code>&lt;PackageReference&gt;</code> node that will allow me to indicate that it is OK for this to target .NET Framework 3.5?</p>
  
  <p><strong>Note:</strong> 
  There's some good info in <a href="http://https:/https://docs.microsoft.com/en-us/nuget/consume-packages/package-references-in-project-files" rel="nofollow noreferrer">Package references (PackageReference) in project files</a>, but it seems it only deals with <code>TargetFramework</code> as a variable to conditionally add references. I don't think I have a mix of .NET Framework versions to deal with - it's just v4.7.2 all the way.</p>