Added support for more optional elements.

Author: shmao

src/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.netcoreapp.cs

@@ -23,6 +23,10 @@ public partial struct XmlUriData
     public partial class SyndicationFeed
     {
         public SyndicationLink Documentation { get{ throw null; } set{ } }
+        public System.Collections.Generic.ICollection<string> SkipDays { get { throw null; } }
+        public System.Collections.Generic.ICollection<int> SkipHours { get { throw null; } }
+        public System.ServiceModel.Syndication.SyndicationTextInput TextInput { get { throw null; } set { } }
+        public int TimeToLive { get { throw null; } set { } }
     }
     public abstract partial class SyndicationFeedFormatter
     {
@@ -31,4 +35,12 @@ public abstract partial class SyndicationFeedFormatter
     }
     public delegate bool TryParseDateTimeCallback(System.ServiceModel.Syndication.XmlDateTimeData data, out System.DateTimeOffset dateTimeOffset);
     public delegate bool TryParseUriCallback(System.ServiceModel.Syndication.XmlUriData data, out System.Uri uri);
+    public partial class SyndicationTextInput
+    {
+        public string Description;
+        public System.ServiceModel.Syndication.SyndicationLink Link;
+        public string Name;
+        public string Title;
+        public SyndicationTextInput() { }
+    }
 }

src/System.ServiceModel.Syndication/src/System/ServiceModel/Syndication/Rss20FeedFormatter.cs

@@ -1027,12 +1027,52 @@ private void WriteFeed(XmlWriter writer)
             }
 
             // Optional spec items
-            // docs
             if (Feed.InternalDocumentation?.Uri != null)
             {
                 writer.WriteElementString(Rss20Constants.DocumentationTag, Feed.InternalDocumentation.Uri.ToString());
             }
 
+            if (Feed.InternalTimeToLive != null)
+            {
+                writer.WriteElementString(Rss20Constants.TimeToLiveTag, Feed.InternalTimeToLive.ToString());
+            }
+
+            if (Feed.InternalSkipHours?.Count > 0)
+            {
+                writer.WriteStartElement(Rss20Constants.SkipHoursTag);
+
+                foreach (int hour in Feed.InternalSkipHours)
+                {
+                    writer.WriteElementString(Rss20Constants.HourTag, hour.ToString());
+                }
+
+                writer.WriteEndElement();
+            }
+
+            if (Feed.InternalSkipDays?.Count > 0)
+            {
+                writer.WriteStartElement(Rss20Constants.SkipDaysTag);
+
+                foreach (string day in Feed.InternalSkipDays)
+                {
+                    writer.WriteElementString(Rss20Constants.DayTag, day);
+                }
+
+                writer.WriteEndElement();
+            }
+
+            if (Feed.InternalTextInput != null)
+            {
+                writer.WriteStartElement(Rss20Constants.TextInputTag);
+
+                writer.WriteElementString(Rss20Constants.DescriptionTag, Feed.InternalTextInput.Description);
+                writer.WriteElementString(Rss20Constants.TitleTag, Feed.InternalTextInput.Title);
+                writer.WriteElementString(Rss20Constants.LinkTag, Feed.InternalTextInput.Link.GetAbsoluteUri().ToString());
+                writer.WriteElementString(Rss20Constants.NameTag, Feed.InternalTextInput.Name);
+
+                writer.WriteEndElement();
+            }
+
             if (_serializeExtensionsAsAtom)
             {
                 _atomSerializer.WriteElement(writer, Atom10Constants.IdTag, this.Feed.Id);