- Every UI component is designed for horizontal text; vertical interfaces require rethinking buttons, toggles, dialogs, and lists.
- Key challenges include sheet animation direction, mixed CJK/Latin content behavior, navigation rail placement, text selection, IME candidate windows, arrow keys meaning, drag-and-drop reordering, and AI chat adaptation.
- Derived principles: respect reading flow, motion should reinforce reading direction, prioritize interaction over typography, design for mixed scripts, ensure accessibility, introduce verticality gradually, and continuously document open research questions.