I think what you're looking for is in the Paint tool. When you have a Paint node selected, look on the left-hand side of the Viewer. You'll see a toolbar that lets you set what mode the tool uses.
- Untitled.png (81.83 KiB) Viewed 6424 times
From top to bottom: Select, Multistroke, Clone Multistroke, Stroke, PolylineStroke, Circle, Rectangle, Copy PolyLine, Copy Circle, Copy Rectangle, Fill, and PaintGroup.
Selecting the PolyLineStroke mode will reveal even more buttons to give you more control over the spline. The Write On control will appear in the Tools panel when PolyLineStroke is selected. Spin down the Stroke Controls section to see it.
Every time you select a new mode button, a stroke modifier will be added to the Modifiers panel for the tool. In Multistroke mode, all of the paint strokes you make are stored in the same Modifier. In Stroke mode, each stroke you make will create a new Modifier. The properties of a paint stroke can be edited after the fact using their Modifiers.
The MaskPaint tool works pretty much the same way.