buchstabe = "a":' NUR A ZULASSEN
 
If Mid$(Text1.Text, 1, 1) <> buchstabe Then Text1.SelStart = 0: Text1.SetFocus
 
pos1 = InStr(1, Text1.Text, ",", 1)
 
If pos1 <> 0 Then pos2 = InStr(pos1 + 1, Text1.Text, ",", 1)
 
If KeyCode = 188 Then Exit Sub
If KeyCode = 32 Then Exit Sub
 
If Mid$(Text1.Text, pos1 + 1, 1) <> buchstabe Then Text1.SelStart = pos1: _
  Text1.SelLength = 1:  'MsgBox "Falscher Buchstabe"

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