package property
The package icon is found in: the file is resolved against its root, and the tooltip over the window's picture names it.
That is all it drives. Nothing reads the package's name or its launcher icon, so naming a package alone would declare nothing a window can show — which is why icon is required beside it.
A Pkg rather than a path string, so it is the same value the plugins below it are configured with and a rename moves one constant.
Implementation
final Pkg package;