The arrangement timeline

The full-width panel along the bottom is the arrangement. It is not a piano roll and not a DAW track view — it edits one on/off flag per layer per song cycle.

What it compiles to

.mask("<1 1 0 1>")

That is the whole representation. Toggle a cell and that layer stops sounding for that cycle; nothing else about the layer changes.

What it draws

Inside each enabled cycle the timeline draws the layer’s real events — evaluated, not guessed — so a cell is not a coloured block but a preview of what will actually be heard.

Gestures

Gesture	Does
Drag the ruler	Set the loop region
Ctrl+wheel	Zoom
Drag the divider	Resize the panel

The loop region matters beyond auditioning: stems render over it. See Export and stems.

Song length

Song length is inferred from the least common multiple of the alternations a song contains, clamped to 64 cycles. That is a starting point rather than a decision — set it explicitly in the timeline whenever the guess is not what you meant.

Imported masks

A flat trailing mask on a layer is lifted into the timeline on import, because a flat mask is an arrangement. Anything more expressive stays an ordinary node in the chain, where you can still see and edit it — the importer does not try to reverse-engineer intent.