At the top of the list(in black writing), you will see the associations which have been defined for the current file type (if any). In addition, in a different color (the color of shadow objects on your Desktop), the associations defined for the parent file types are also displayed. As a result, this container displays pretty much the same as the "Open" submenu of a data file of the current type.
This container accepts program objects being dropped
on it (that is, objects of the WPProgram and WPProgramFile classes).
Also, you can rearrange the order of associations within the container
using drag'n'drop, but only for the items displayed in black color.