KDE .desktop keyword documentation

[lmuserx4849]

Does anyone know where the keywords are documented for .desktop files in a KDE environment?

I know about: http://standards.freedesktop.org/menu-s ... c-1.1.html. It has helped a little. Most of my googling has taken me to sites that show a desktop file,
but don't explain where they got the information. It looks like a lot of cloning of code. I'd like to understand and build my own.

Some examples of keywords I'm looking for doc: X-KDE-SubstituteUID, X-KDE-Username, X-KDE-Priority, X-KDE-Submenu. I've found bits and pieces of doc here and there.

I know some sort of substitution is going on here, but what is the $e: Path[$e]=

In KMenu what directs a particular .desktop/application to a particular menu. A specific Categories keyword contains "Application;Development;Java", but it isn't being placed
in the Application -> Development -> Java submenu.

When I use the KDE Menu editor (right-click KMenu -> Edit Applications), I see the results written to $HOME/.config/menus. Quick and dirty I suppose I could edit
that file, but can't I create a application's .desktop file that would create a new menu -> submenu.

My searches are finding the same info and I'm kind of stuck. Any pointers would be appreciated.