Some (text?) input UI elements can have placeholder content if there is no user input content currently.
It would be good to have some guides what to display there and in what style.
Sections where one would expect some notes about placeholder text:
- https://hig.kde.org/style/writing/capitalization.html
- https://hig.kde.org/components/lineedit.html
- https://hig.kde.org/components/textedit.html
Examples of code components with such a feature: