I need some information which you do not find by google (or find contradictory sources)
on Kubuntu - KDE 4.13:

what is KDEDIR
Is there at least a clear "definition" of where it should point to? there seems to be as many answers as the number of question you ask about it

when installing a new-home made application, what is the normal process ?
install it to usr/share
install it to usr/local

you make a plasmoid following this https://techbase.kde.org/Development/Tutorials/Plasma4/GettingStarted
how do you install it?
why does it go to /usr/local/lib/kde4 while there is no other plasmoid in there ?
why plasmaviewer can not find it? even though you kbuilsyscoca4
you move it manually to /usr/share/kde4/apps/plasma/plasmoids , you kbuildsyscoca4 it as much as you want, it still does not find it. Why?
Why two places to store one thing?

Apparently plasmoid can be made with Python QML C++ Java, What is/should be the standard (aka what is the most used)

Is KxmlGuiWindow the most up to date way to generate kde application or has it been superseeded? https://techbase.kde.org/Development/Tutorials/Using_KActions