Just adding docs

src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/RequiresPreviewFeaturesAttribute.cs

@@ -17,15 +17,28 @@ namespace System.Runtime.Versioning
                 AttributeTargets.Event, Inherited = false)]
     public sealed class RequiresPreviewFeaturesAttribute : Attribute
     {
+        /// <summary>
+        /// Initializes a new instance of the <seealso cref="RequiresPreviewFeaturesAttribute"/> class.
+        /// </summary>
         public RequiresPreviewFeaturesAttribute() { }
 
+        /// <summary>
+        /// Initializes a new instance of the <seealso cref="RequiresPreviewFeaturesAttribute"/> class with the specified message.
+        /// </summary>
+        /// <param name="message">An optional message associated with this attribute instance.</param>
         public RequiresPreviewFeaturesAttribute(string? message)
         {
             Message = message;
         }
 
+        /// <summary>
+        /// Returns the optional message associated with this attribute instance.
+        /// </summary>
         public string? Message { get; }
 
+        /// <summary>
+        /// Returns the optional URL associated with this attribute instance.
+        /// </summary>
         public string? Url { get; set; }
     }
 }