reset ObsoleteAttribute

Author: gewarren

xml/System/ObsoleteAttribute.xml

@@ -69,14 +69,18 @@
     </Attribute>
   </Attributes>
   <Docs>
-    <summary>
-            Marks program elements that are no longer in use.
-            </summary>
+    <summary>Marks the program elements that are no longer in use. This class cannot be inherited.</summary>
     <remarks>
-            Source code imported from 
-            <see href="https://github.com/dotnet/runtime/blob/5535e31a712343a63f5d7d796cd874e563e5ac14/src/libraries/System.Private.CoreLib/src/System/ObsoleteAttribute.cs">
-            ObsoleteAttribute.cs</see> without any changes, all resulting warnings ignored accordingly.
-            </remarks>
+      <format type="text/markdown"><![CDATA[
+<xref:System.ObsoleteAttribute> is applicable to all program elements except assemblies, modules, parameters, and return values. Marking an element as obsolete informs users that the element may be removed in a future version of the product.
+
+The string assigned to the <xref:System.ObsoleteAttribute.Message> property is emitted by the compiler when the attribute target is used in code. Ideally, the string should provide some workaround or programmatic alternative.
+
+Use the <xref:System.ObsoleteAttribute.IsError> property to indicate to the compiler whether using the <xref:System.ObsoleteAttribute> attribute should cause it to emit an error (<xref:System.ObsoleteAttribute.IsError%2A> is `true`) or a warning (<xref:System.ObsoleteAttribute.IsError%2A> is `false`).
+
+For more information about using attributes, see [Attributes](/dotnet/standard/attributes/).
+      ]]></format>
+    </remarks>
     <example>
       <format type="text/markdown"><![CDATA[
 The following example defines a class that contains a property and a method that are marked with the <xref:System.ObsoleteAttribute> attribute. Accessing the value of the `OldProperty` property in code generates a compiler warning, but calling the `CallOldMethod` method generates a compiler error. The example also shows the output that results when you attempt to compile the source code.