public void Complete(ICSharpCode.AvalonEdit.Editing.TextArea textArea, ISegment completionSegment, EventArgs insertionRequestEventArgs) { var word = QueryComposerHelper.ExtractPreviousWord(textArea.Document.Text, completionSegment.EndOffset - 1); ISegment replaceSegment = completionSegment; if (stringval.Substring(0, word.Length) == word) { replaceSegment = new CustomSegment(completionSegment.EndOffset - word.Length, word.Length); } textArea.Document.Replace(replaceSegment, stringval); }