title: .NET Core - XElement could not be found when targeting .NET Framework 4.6
body: <p>I'm having a weird problem when using XElement in .NET Core project und targeting .NET Framework 4.6. I've made a very simple project to reproduce the error.</p>
  
  <ol>
  <li><p>I create a standard library project with only one class.</p>
  
  <pre><code>public class Class1
  {
      public Class1()
      {
          XElement element = null;
      }
  }
  </code></pre></li>
  <li><p>And in my project.json, I would like to target .net core and .net framework 4.6</p>
  
  <pre><code> {
     "version": "1.0.0-*",
  
     "dependencies": {
       "NETStandard.Library": "1.6.0",
      "System.Xml.XmlDocument": "4.3.0"
     },
  
     "frameworks": {
       "netstandard1.6": {
         "imports": "dnxcore50"
       },
       "net46": {
       }
     }
   }
  </code></pre></li>
  </ol>
  
  <p>When I compile the project, I always receive the error "<em>The type or namespace name 'XElement' could not be found (are you missing a using directive or an assembly reference?)</em>" (this error happens only with .NET Framework 4.6)</p>
  
  <p>I have no idea why it doesn't compile. I've tried to create a Console Application with .net framework 4.6 and add reference to System.Xml.XmlDocument and it works. Only with .NET core project, it doesn't.</p>
  
  <p>Thank you.</p>