private void OnDocumentLoaded(object sender, DocumentDataEventArgs e)
        {
            if (!e.IsPWEDoc)
            {
                return;
            }

            var pweDoc = (IPWEDoc)e.Document;

            pweDoc.TextChanging += this.PweDoc_TextChanging;
        }
        private void OnClosingDocument(object sender, DocumentDataEventArgs e)
        {
            if (!e.IsPWEDoc)
            {
                return;
            }

            var pweDoc = (IPWEDoc)e.Document;

            try
            {
                pweDoc.TextChanging -= this.PweDoc_TextChanging;
            }
            catch (Exception)
            {
                // ignored
            }
        }