Add at least basic class level docs for several controls.

src/Avalonia.Controls/DateTimePickers/TimePicker.cs

@@ -8,7 +8,7 @@ using System.Globalization;
 namespace Avalonia.Controls
 {
     /// <summary>
-    /// A control to allow the user to select a time
+    /// A control to allow the user to select a time.
     /// </summary>
     [PseudoClasses(":hasnotime")]
     public class TimePicker : TemplatedControl

src/Avalonia.Controls/Expander.cs

@@ -4,14 +4,35 @@ using Avalonia.Controls.Primitives;
 
 namespace Avalonia.Controls
 {
+    /// <summary>
+    /// Direction in which an <see cref="Expander"/> control opens.
+    /// </summary>
     public enum ExpandDirection
     {
+        /// <summary>
+        /// Opens down.
+        /// </summary>
         Down,
+
+        /// <summary>
+        /// Opens up.
+        /// </summary>
         Up,
+
+        /// <summary>
+        /// Opens left.
+        /// </summary>
         Left,
+
+        /// <summary>
+        /// Opens right.
+        /// </summary>
         Right
     }
 
+    /// <summary>
+    /// A control with a header that has a collapsible content section.
+    /// </summary>
     [PseudoClasses(":expanded", ":up", ":down", ":left", ":right")]
     public class Expander : HeaderedContentControl
     {

src/Avalonia.Controls/Grid.cs

@@ -17,7 +17,7 @@ using Avalonia.VisualTree;
 namespace Avalonia.Controls
 {
     /// <summary>
-    /// Grid
+    /// Defines a flexible grid area that consists of columns and rows.
     /// </summary>
     public class Grid : Panel
     {

src/Avalonia.Controls/Primitives/ScrollBarVisibility.cs

@@ -1,10 +1,28 @@
 namespace Avalonia.Controls.Primitives
 {
+    /// <summary>
+    /// Specifies the visibility of a <see cref="ScrollBar"/> for scrollable content.
+    /// </summary>
     public enum ScrollBarVisibility
     {
+        /// <summary>
+        /// No scrollbars and no scrolling in this dimension.
+        /// </summary>
         Disabled,
+
+        /// <summary>
+        /// The scrollbar should be visible only if there is more content than fits in the viewport.
+        /// </summary>
         Auto,
+
+        /// <summary>
+        /// The scrollbar should never be visible.  No space should ever be reserved for the scrollbar.
+        /// </summary>
         Hidden,
+
+        /// <summary>
+        /// The scrollbar should always be visible.  Space should always be reserved for the scrollbar.
+        /// </summary>
         Visible,
     }
 }

src/Avalonia.Controls/RadioButton.cs

@@ -8,6 +8,9 @@ using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
 {
+    /// <summary>
+    /// Represents a button that allows a user to select a single option from a group of options.
+    /// </summary>
     public class RadioButton : ToggleButton
     {
         private class RadioButtonGroupManager

src/Avalonia.Controls/RelativePanel.cs

@@ -8,6 +8,9 @@ using Avalonia.Layout;
 
 namespace Avalonia.Controls
 {
+    /// <summary>
+    /// Defines an area within which you can position and align child objects in relation to each other or the parent panel.
+    /// </summary>
     public partial class RelativePanel : Panel
     {
         private readonly Graph _childGraph;

src/Avalonia.Controls/RepeatButton.cs

@@ -4,6 +4,9 @@ using Avalonia.Threading;
 
 namespace Avalonia.Controls
 {
+    /// <summary>
+    /// Represents a control that raises its <see cref="Button.Click"/> event repeatedly when it is pressed and held.
+    /// </summary>
     public class RepeatButton : Button
     {
         /// <summary>

src/Avalonia.Controls/TextBox.cs

@@ -17,6 +17,9 @@ using Avalonia.Controls.Metadata;
 
 namespace Avalonia.Controls
 {
+    /// <summary>
+    /// Represents a control that can be used to display or edit unformatted text.
+    /// </summary>
     [PseudoClasses(":empty")]
     public class TextBox : TemplatedControl, UndoRedoHelper<TextBox.UndoRedoState>.IUndoRedoHost
     {