2018-08-02

The bottom notches include a margin, a specified tab length, and a specified
number of tabs.  The pitch between tab centers is computed and rounded down to
the nearest integer as follows:

  pitch = int((panel - margin) / tab_count)

= int ( ( "x_panel@front layout" - "x_margin@front layout" ) / "x_tab_count@front layout" )
= int ( ( "y_panel@front layout" - "y_margin@front layout" ) / "y_tab_count@front layout" )

For the side, the calcuation is slightly different:

  pitch = int((inner - 2*margin - tab_length) / (tab_count-1))