Meaning of Empty Grouping Plasmoid and Empty System Tray in desktop contexts menu

[Mincho Kondarev]

Hello, 
when checking the translation in Bulgarian, I noticed that in contexts  menu 
(by right clicking on desktop)  in entry Add panel there are subentries 
Empty Grouping Plasmoid and Empty System Tray. Choosing them nothing happens. 
What is the purpose of these entries? Where are those empty elements  located 
on desktop?  I am not sure how to translate them.