[DefaultMember("Item")]
public class ThreadCommentCollection : WorksheetElement 

using( var workbook = Workbook.Create( "AddComment.xlsx" ) ) 
  { 
    // Gets the first Worksheet; a Workbook always contains at least 1 Worksheet. 
    var worksheet = workbook.Worksheets[ 0 ]; 

    // Gets the annotations collection. 
    var annotations = worksheet.Annotations; 

    // Adds a Comment attached to Cell B1. 
    var comment = annotations.AddComment( "This is the title of the document", "B1" ); 

    // Replies to the Comment. 
    comment.Reply( "Wait I can also be in the thread of the conversation ?" ); 

    // Gets the thread of Comments. 
    var threadCommentCollection = annotations.Comments; 

    // Gets the number of Comments in the thread for Cell "B1". 
    var thread1_Count = threadCommentCollection[ "B1" ].Count; 

    // Saves Workbook to disk; 
    workbook.Save(); 
  }