title: Reference for msbuild itemgroup content
body: <p>I several times had trouble finding information about valid elements in csproj files (.NET Core). Especially ItemGroup with Content and Include/Exclude/Update/CopyToPublishDirectory attributes.
  Also I am interested in "None Include=..." elements.</p>
  
  <p>Is there any offical reference for all this?</p>
  
  <p>At least I could only find a few SO posts.</p>
  
  <p><strong>Update</strong></p>
  
  <p>in the meantime I found this upgrade guide (project.json -> csproj) by Nate McMaster which contains a few examples for Content and None but is far from a reference.</p>
  
  <p><a href="https://docs.microsoft.com/en-us/dotnet/core/tools/project-json-to-csproj" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/dotnet/core/tools/project-json-to-csproj</a></p>