In ArchiCAD 12, Window objects were enhanced to include a new set of parameters, classed as the "Custom Corner" function.
This essentially made the existing 'Corner Window' tool redundant and improved dramatically the ability to create a corner window arrangement.

To create a corner window arrangement, the following is required:

1. A set of two walls joined a corner
2. Two independently placed windows on each side of the corner
3. Each window has its own Custom Corner parameters setup to create the appropriately chamfered window end
4. Each window is then moved into position to to form the corner

Windows can also be chamfered in opposite directions to form a chain of Corner Windows.

In a sample ArchiCAD 12 PLN (available here), a number of arrangements have setup:

• The classic Corner Window
• The classic Bay Window
• The Z-shaped arrangement

In each arrangement note that all the window elements are ALL different window objects, each customisable.
No longer are Corner Windows related (and then prone to disconnecting under certain circumstances), which allows the user a much wider range of freedom in design.

This new functionality is one of the most productive improvements in ArchiCAD 12.