Does anyone know what these blue lines mean in Animation Sequencer?

[zhutianci123]

Does anyone know what these blue lines mean(red arrow)?

[Max.Chen]

Those are Frame Markers

Using Frame Markers in Sequencer

[zhutianci123]

It isn’t Frame Marker. It is called Selection Range. Thanks by the way.

[Max.Chen]

Ah, yes. You’re right!