racket - What does DrRacket mean by reverse video in the definitions window (after pressing Run)?

Question

I've written a small module in Beginning Student Language. When I click Run, some expressions in the Definitions window are highlighted in reverse video (red text on a black background). I can't figure out which expressions are chosen or what the reverse video means.

Answer 1

根据颜色偏好，它表示测试未涵盖的代码：