public static async Task<bool> IsValid (MonoDevelop.Ide.Gui.Document doc, CancellationToken cancellationToken = default(CancellationToken))
		{
			if (doc == null)
				return false;
			if (doc.Editor == null || !doc.Editor.IsSomethingSelected)
				return false;
			var ad = doc.AnalysisDocument;
			if (ad == null)
				return false;
			var selectionRange = doc.Editor.SelectionRange;
			try {
				var selection = new CSharpSelectionValidator (await SemanticDocument.CreateAsync (ad, cancellationToken).ConfigureAwait (false), new TextSpan (selectionRange.Offset, selectionRange.Length), doc.GetOptionSet ());
				var result = await selection.GetValidSelectionAsync (cancellationToken).ConfigureAwait (false);
				return result.ContainsValidContext;
			} catch (Exception) {
				return false;
			}
		}
		public async static Task Run (MonoDevelop.Ide.Gui.Document doc)
		{
			if (!doc.Editor.IsSomethingSelected)
				return;
			var ad = doc.AnalysisDocument;
			if (ad == null)
				return;
			try {
				var selectionRange = doc.Editor.SelectionRange;
				var token = default(CancellationToken);
				var selection = new CSharpSelectionValidator (await SemanticDocument.CreateAsync (ad, token).ConfigureAwait (false), new TextSpan (selectionRange.Offset, selectionRange.Length), doc.GetOptionSet ());
				var result = await selection.GetValidSelectionAsync (token).ConfigureAwait (false);
				if (!result.ContainsValidContext)
					return;
				var extractor = new CSharpMethodExtractor ((CSharpSelectionResult)result);
				var extractionResult = await extractor.ExtractMethodAsync (token).ConfigureAwait (false);
				var changes = await extractionResult.Document.GetTextChangesAsync (ad, token);
				using (var undo = doc.Editor.OpenUndoGroup ()) {
					foreach (var change in changes.OrderByDescending (ts => ts.Span.Start)) {
						doc.Editor.ReplaceText (change.Span.Start, change.Span.Length, change.NewText);
					}
					// hack to remove the redundant private modifier.
					if (doc.Editor.GetTextAt (extractionResult.MethodDeclarationNode.SpanStart, "private ".Length) == "private ") {
						doc.Editor.RemoveText (extractionResult.MethodDeclarationNode.SpanStart, "private ".Length);
					}
				}
				doc.UpdateParseDocument ();
				var info = RefactoringSymbolInfo.GetSymbolInfoAsync (doc, extractionResult.InvocationNameToken.Span.Start).Result;
				var sym = info.DeclaredSymbol ?? info.Symbol;
				if (sym != null)
					new MonoDevelop.Refactoring.Rename.RenameRefactoring ().Rename (sym);
			}
			catch (Exception e) {
				LoggingService.LogError ("Error while extracting method", e);
			}
		}