The "Modern Viewport" was an option in the Viewport panel that would use
the new fancy wire frame code and some depth debugging functionality.
This was introduced as a quick and dirty way to get the new drawing
system showing in the viewport.
Overtime we built a complete Draw Manager system, leaving this original
approach deprecated which adds clutter to Blender code since it would be
removed sooner or later.
Note: The new fancy wireframes and related shaders (white out other
objects) are still in Blender code, though you can't use them anymore.
If we are to have any of those drawing options they should be integrated
in the new draw manager, instead of integrated in the old drawing
pipeline as it was originally coded.
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