tutor chars --import <file>.Dotted underline = tone sandhi — the syllable's tone shifts in connected speech (tap/hover for why).
New characters in this lesson — tap a character to see its strokes drawn, or ✎ to trace it yourself. (Needs internet for now.)
Definitions from CC-CEDICT (CC BY-SA 4.0). Example sentences from 教育部《重編國語辭典修訂本》 via 萌典 (g0v moedict) (CC BY-ND 3.0 TW).