Private Function IndexOf_UIntegerValue _
             (ByVal str As String, number As UInteger, _
              Optional ByVal startindex As Integer = 0, _
              Optional ByVal count As Integer = -1) As Integer
 
        Const ziffern As String = "0123456789"
 
        If str Is Nothing Then Return -1
        startindex = Math.Max(startindex, 0)
 
        Dim index As Integer
        If count > 0 Then
            index = str.IndexOf(number.ToString, startindex, count)
        Else
            index = str.IndexOf(number.ToString, startindex)
        End If
 
        If index = -1 Then Return -1 'Ziffernfolge nicht gefunden
 
        Dim startok, endok As Boolean
        If index = 0 Then
            startok = True 'Ziffernfolge steht am Anfang
        Else
            startok = Not ziffern.Contains(str.Substring(index - 1, 1))
        End If
 
        Dim nextindex As Integer = index + number.ToString.Length
        If nextindex = str.Length Then
            endok = True 'Ziffernfolge steht am Ende
        Else
            endok = Not ziffern.Contains(str.Substring(nextindex, 1))
        End If
 
        If startok And endok Then Return index
        Return -1
    End Function