System.IO.Packaging docs

Author: ericstj

xml/System.IO.Packaging/Package.xml

@@ -1278,6 +1278,8 @@ For more information about packages and package parts, see section 1.1 of the Op
             <see cref="M:System.IO.Packaging.Package.GetParts" /> internally calls the derived class <see cref="M:System.IO.Packaging.Package.GetPartsCore" /> method to actually flush the part based on the physical format implemented in the derived class.</para>
         </block>
         <altmember cref="M:System.IO.Packaging.Package.GetPart(System.Uri)" />
+        <exception cref="T:System.IO.FileFormatException">The package has a bad format.</exception>
+        <exception cref="T:System.InvalidOperationException">The part name prefix exists.</exception>
       </Docs>
     </Member>
     <Member MemberName="GetPartsCore">