Add comments copied from VisualExtensions.

src/Avalonia.Styling/LogicalTree/LogicalExtensions.cs

@@ -3,8 +3,16 @@ using System.Collections.Generic;
 
 namespace Avalonia.LogicalTree
 {
+    /// <summary>
+    /// Provides extension methods for working with the logical tree.
+    /// </summary>
     public static class LogicalExtensions
     {
+        /// <summary>
+        /// Enumerates the ancestors of an <see cref="ILogical"/> in the logical tree.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <returns>The logical's ancestors.</returns>
         public static IEnumerable<ILogical> GetLogicalAncestors(this ILogical logical)
         {
             Contract.Requires<ArgumentNullException>(logical != null);
@@ -18,6 +26,11 @@ namespace Avalonia.LogicalTree
             }
         }
 
+        /// <summary>
+        /// Enumerates an <see cref="ILogical"/> and its ancestors in the logical tree.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <returns>The logical and its ancestors.</returns>
         public static IEnumerable<ILogical> GetSelfAndLogicalAncestors(this ILogical logical)
         {
             yield return logical;
@@ -57,11 +70,21 @@ namespace Avalonia.LogicalTree
             return null;
         }
 
+        /// <summary>
+        /// Enumerates the children of an <see cref="ILogical"/> in the logical tree.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <returns>The logical children.</returns>
         public static IEnumerable<ILogical> GetLogicalChildren(this ILogical logical)
         {
             return logical.LogicalChildren;
         }
 
+        /// <summary>
+        /// Enumerates the descendants of an <see cref="ILogical"/> in the logical tree.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <returns>The logical's ancestors.</returns>
         public static IEnumerable<ILogical> GetLogicalDescendants(this ILogical logical)
         {
             foreach (ILogical child in logical.LogicalChildren)
@@ -75,6 +98,11 @@ namespace Avalonia.LogicalTree
             }
         }
 
+        /// <summary>
+        /// Enumerates an <see cref="ILogical"/> and its descendants in the logical tree.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <returns>The logical and its ancestors.</returns>
         public static IEnumerable<ILogical> GetSelfAndLogicalDescendants(this ILogical logical)
         {
             yield return logical;
@@ -107,16 +135,34 @@ namespace Avalonia.LogicalTree
             return FindDescendantOfTypeCore<T>(logical);
         }
 
+        /// <summary>
+        /// Gets the logical parent of an <see cref="ILogical"/>.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <returns>The parent, or null if the logical is unparented.</returns>
         public static ILogical GetLogicalParent(this ILogical logical)
         {
             return logical.LogicalParent;
         }
 
+        /// <summary>
+        /// Gets the logical parent of an <see cref="ILogical"/>.
+        /// </summary>
+        /// <typeparam name="T">The type of the logical parent.</typeparam>
+        /// <param name="logical">The logical.</param>
+        /// <returns>
+        /// The parent, or null if the logical is unparented or its parent is not of type <typeparamref name="T"/>.
+        /// </returns>
         public static T GetLogicalParent<T>(this ILogical logical) where T : class
         {
             return logical.LogicalParent as T;
         }
 
+        /// <summary>
+        /// Enumerates the siblings of an <see cref="ILogical"/> in the logical tree.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <returns>The logical siblings.</returns>
         public static IEnumerable<ILogical> GetLogicalSiblings(this ILogical logical)
         {
             ILogical parent = logical.LogicalParent;
@@ -130,6 +176,15 @@ namespace Avalonia.LogicalTree
             }
         }
 
+        /// <summary>
+        /// Tests whether an <see cref="ILogical"/> is an ancestor of another logical.
+        /// </summary>
+        /// <param name="logical">The logical.</param>
+        /// <param name="target">The potential descendant.</param>
+        /// <returns>
+        /// True if <paramref name="logical"/> is an ancestor of <paramref name="target"/>;
+        /// otherwise false.
+        /// </returns>
         public static bool IsLogicalAncestorOf(this ILogical logical, ILogical target)
         {
             ILogical current = target?.LogicalParent;