Public Function MaxLineWidth(ByVal hWnd As Long) As Long
 
   Dim lmLineCounter       As Long
   Dim lmLen               As Long
   Dim smLineText          As String
   Dim I                   As Integer
 
   ' zunächst die Anzahl der Zeilen ermitteln
   lmLineCounter = SendMessage(hWnd, EM_GETLINECOUNT, 0, 0&)
 
   For I = 1 To lmLineCounter
      smLineText = Space$(1024)
      lmLen = SendMessage(hWnd, EM_GETLINE, I - 1, smLineText)
      smLineText = Left$(smLineText, lmLen)
 
      If frmMsgBox.TextWidth(smLineText) > MaxLineWidth Then
         MaxLineWidth = frmMsgBox.TextWidth(smLineText)
         DoEvents
      End If
      DoEvents
   Next
 
End Function