Add some documentation comments.

ICSharpCode.NRefactory/CSharp/Ast/AstNode.cs

@@ -578,6 +578,19 @@ namespace ICSharpCode.NRefactory.CSharp
 		public abstract S AcceptVisitor<T, S> (IAstVisitor<T, S> visitor, T data);
 		
 		#region Pattern Matching
+		/// <summary>
+		/// Performs a pattern matching operation.
+		/// <c>this</c> is the pattern, <paramref name="other"/> is the AST that is being matched.
+		/// </summary>
+		/// <returns>
+		/// If successful, a match object containing the matched groups.
+		/// If the match failed, returns <c>null</c>.
+		/// </returns>
+		/// <remarks>
+		/// Patterns are ASTs that contain special pattern nodes (from the PatternMatching namespace).
+		/// However, it is also possible to match two ASTs without any pattern nodes - doing so will produce an empty match object
+		/// if the two ASTs are structurally identical; or will return <c>null</c> if the ASTs are not identical.
+		/// </remarks>
 		public Match Match(AstNode other)
 		{
 			Match match = new Match();

ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Backreference.cs

@@ -6,6 +6,9 @@ using System.Linq;
 
 namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 {
+	/// <summary>
+	/// Matches the last entry in the specified named group.
+	/// </summary>
 	public class Backreference : Pattern
 	{
 		readonly string referencedGroupName;

ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Match.cs

@@ -7,7 +7,10 @@ using System.Linq;
 
 namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 {
-	public class Match
+	/// <summary>
+	/// Represents the result of a pattern matching operation.
+	/// </summary>
+	public sealed class Match
 	{
 		List<KeyValuePair<string, AstNode>> results = new List<KeyValuePair<string, AstNode>>();
 		

ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Pattern.cs

@@ -5,6 +5,9 @@ using System;
 
 namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 {
+	/// <summary>
+	/// Base class for all patterns.
+	/// </summary>
 	public abstract class Pattern : AstNode
 	{
 		public override NodeType NodeType {