If the Document is changed without using transactions, each time any of the NodeInserted, NodeRemoved and NodeChanged events of the XmlDocument occurs, the control performs synchronization between XML and MSHTML. Calling BeginTransaction(string) tells the control it must not synchronized any changes made in XmlDocument until CommitTransaction() is called. The ApplyStyle(string, string) and the RemoveStyle(string, string) methods of the C1TextRange automatically start a transaction, if it has not been started yet.