title: Missing XmlSchemaSet UWP
body: <p>I'm trying to validate a xmldocument against a Xsd schema in UWP targeting Windows 10, but I'm unable to find XmlSchemaSet class and all the related methods. </p>
  
  <p>System.Xml.Schema namespace seems to be incomplete. </p>
  
  <p>Referenced assembly is System.Xml.ReaderWriter, Version=4.0.10.0</p>
  
  <p>Is there any package to import?</p>
  
  <p>thanks</p>