public void Cancel()

Public Sub Cancel

void OnCustomMask(object sender, DevExpress.Xpf.Editors.CustomMaskEventArgs e) {
    if (e.IsCanceled || e.ResultEditText.Length < e.CurrentEditText.Length || 
        e.ActionType == CustomTextMaskInputAction.Init || e.ResultEditText.Length <= 5)
        return;
    if (e.CurrentEditText.Length == 5 && e.CurrentSelectedText == String.Empty) {
        e.Cancel();
        return;
    }
    var maxInsertLength = 5 - e.CurrentHead.Length - e.CurrentTail.Length;
    e.SetResult(e.CurrentHead + e.InsertedText.Substring(0, maxInsertLength), e.CurrentTail);
}

Private Sub OnCustomMask(ByVal sender As Object, ByVal e As DevExpress.Xpf.Editors.CustomMaskEventArgs)
    If e.IsCanceled OrElse e.ResultEditText.Length < e.CurrentEditText.Length OrElse e.ActionType = CustomTextMaskInputAction.Init OrElse e.ResultEditText.Length <= 5 Then Return

    If e.CurrentEditText.Length = 5 AndAlso e.CurrentSelectedText = String.Empty Then
        e.Cancel()
        Return
    End If

    Dim maxInsertLength = 5 - e.CurrentHead.Length - e.CurrentTail.Length
    e.SetResult(e.CurrentHead + e.InsertedText.Substring(0, maxInsertLength), e.CurrentTail)
End Sub