Public Function GetMenuItem(sessionProfile As SessionProfile) As MenuButton() Implements IPluginMenuExtender.GetMenuItem
...
      Dim btnMenu_01b_tools8 = New MenuButton("Minus Plus (∓)", AddressOf Me.OnClick_InsertMinusPlus)
      btnMenu_01b_tools8.Behavior = MenuButtonBehavior.AlwaysEnabled
      btnMenu_01b_tools8.ShortcutKey = InputKeys.Control Or InputKeys.Subtract ' https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.keys?view=windowsdesktop-7.0
...
      Return (New MenuButton() {btnMenu_01c, btnMenu_01d, btnMenu_01g, btnMenu_01h, btnMenu_01_tools})
   End Function

   Public Sub OnClick_InsertMinusPlus(_args As MenuButtonArgs)
      Try
         If IsNothing(_args.CurrentRegion) Then
            Dim Lourdes As SMath.Controls.MathRegion = New SMath.Controls.MathRegion(_args.SessionProfile)
            Dim expr = New List(Of SMath.Manager.Term) 'As SMath.Manager.Term() ' = {} '
            expr.Add(New SMath.Manager.Term("#", SMath.Manager.TermType.Operand, 0))
            expr.Add(New SMath.Manager.Term("∓", SMath.Manager.TermType.Operator, 1))

            Lourdes.Terms = expr.ToArray

            Dim Avignon As SMath.Controls.RegionsEnumerator = New SMath.Controls.RegionsEnumerator(New List(Of SMath.Controls.RegionBase)({Lourdes}), 0)
            _args.Worksheet.CreateRegions(Avignon, 0, 0, , )
         Else
            _args.CurrentRegion.OnCommandSend("∓"
         End If
      Catch ex As Exception
         MsgBox(ex.ToString())
      End Try
   End Sub