There a re a lot of pages int he HIG that contain information on the usage and layout for lists:
- https://community.kde.org/KDE_Visual_Design_Group/HIG/ListView
- https://community.kde.org/KDE_Visual_Design_Group/HIG/SOU_Workspace#Design_Patterns
- https://community.kde.org/KDE_Visual_Design_Group/HIG/DualList
- https://community.kde.org/KDE_Visual_Design_Group/HIG/Contributing#Selection
Some of the pages are only drafts, some are conflicting and a lot of information especially regarding the layout are missing.