Mark area.

A reusable selection. Drag to mark triangles in teal-green. The marked set isn't paint — it's a scope. You can Paint marked area, run Simplify on just it, or run Clean edges on just it.

Same brush filters as the Brush tool apply: Stop at colour change, Stop at crease, Sharp above.

• You want to paint and then clean up the same area without re-selecting.
• Scoping Simplify so only one busy region loses triangles.
• Scoping Clean edges so it doesn't bleed through thin walls elsewhere.
• Painting an irregular area that's not one region and isn't clean enough for Brush filters.

1. Press P until Mark area.
2. Drag across the area. Teal-green overlay marks each triangle.
3. Unmark with Shift+drag. Trim the edges of the selection.
4. Enable filters to keep marks inside a colour band or behind a crease.
5. Act on it. A floating bar appears on the model — hit Paint marked area there to flood the mark with the active colour (it commits on the canvas now, not from the side panel). Or jump to the Check tab → Clean edges, or the Export tab → Simplify now, to scope those to the mark.

• Marked tris persist across tool switches until you Clear. If Simplify or Clean edges acts on a smaller area than expected, you may have a stale mark.
• Brush ignores the mark. Only Paint marked area — on the floating bar over the model — uses it as a scope.
• Filters too tight? Raise Sharp above if Stop at crease misses places you wanted to mark.