Format Textbox à la saisie

Option Explicit
Private Sub Tsiret_KeyDown(ByVal KeyCode As MSForms.ReturnInteger, ByVal Shift As Integer)
    Dim Mask$, txt$, s&, longg&, plus&
    Mask = "XXX / XXX XX XX"
       If Tsiret = "" And KeyCode <> 8 And KeyCode <> 46 Then Tsiret = Mask
    txt = Tsiret.Value:    If txt = Mask Then Tsiret.SelStart = 0
    s = Tsiret.SelStart:
    longg = Tsiret.SelLength: If longg = 0 Then longg = 1
    plus = IIf(KeyCode < 96, 32, -48):
    Select Case KeyCode
    Case 96 To 105,65 to 90
        If s = Len(Mask) Then KeyCode = 0: Exit Sub
        If Mid(Mask, s + 1, 1) <> "X" Then KeyCode = 0: s = s + 1: Tsiret.SelStart = s: Exit Sub
        Mid(txt, s + 1, longg) = Chr(KeyCode + plus) & Mid(Mask, s + 2, longg - 1): KeyCode = 0
        Tsiret = txt: Tsiret.SelStart = IIf(InStr(1, Tsiret, "X") = 0, s + 1, InStr(1, Tsiret, "X") - 1)
    Case 8
        If s <> 0 Then Mid(txt, s, longg + 1) = Mid(Mask, s, longg + 1) Else Exit Sub
        Tsiret = txt: Tsiret.SelStart = s - 1: KeyCode = 0
        If txt = Mask Then Tsiret = ""
    Case 46
        If Tsiret = "" Then Exit Sub
        If longg = 0 Then longg = 1
        Mid(txt, s + 1, longg) = Mid(Mask, s + 1, longg)
        Tsiret = txt: Tsiret.SelStart = s: KeyCode = 0
        If txt = Mask Then Tsiret = ""

    Case 39: Tsiret.SelStart = s + 1
    Case 37: Tsiret.SelStart = s - IIf(s > 0, 1, 0)
    Case 13:    ' touche enter  fait ce que tu veux c'est la sortie
    Case Else: KeyCode = 0
    End Select
End Sub