**Intro**
[MiHa] 2015-06-06:
[Invoice-Demo] was a nice small demo of a simple program using only basic, essential GUI-features:
   * Menu
   * Buttons (to see them, change that "if 0"-section to "if 1")
   * Hotkeys (F1..F9, etc.)
   * Labels
   * Entry-fields
   * Messagebox
   * Title at top of window
   * Icon at top of window (currently, this needs an external file)
   * [frame]s, [pack] and [grid] to manage the layout

There is lots of more advanced GUI-stuff not covered in that program, e.g.:
   * Checkboxes
   * Radiobuttons
   * Fancy textformating, [font]s (i.e. for a nice help-window)
   * http://wiki.tcl.tk/1437%|%Listbox%|% / [Multicolumn listbox] / [Tables]
   * Scrollbars
   * dialog-windows separate from the main-window (i.e. for the data-entry form)

Some of that stuff will go into this version 2
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**Program**
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