Adjusting sound volume. How do I see the frames?

About adjusting a sound’s volume, the guide says:
"In the Current Sound panel, click on the thin blue line above waveform to add an envelope marker. Drag the envelope markers to adjust the volume at that frame and to create the time of the transition"

As far as I can see, whereas the Sound Element panel shows frames, the Current Sound panel tells me where I am only in milliseconds. I can’t see frames anywhere.
What am I to do if I want to change the volume handles at a given frame?

I’m sure I’m not seeing something really obvious and when I get the answer I’ll feel really dumb, but I swear I haven’t found a way to visualize the frames.

thank you

Aha, at last I found it!
It’s those flag-like markers. I hadn’t seen them straight away.

I’ll leave this post, you never know someone might have the same question…