slider

A parameter the reader drags along a track, surfaced as a row in the scene's footer. It declares the parameter as well as offering it: slider:a(range: [0, 5]) is the letter a between 0 and 5, and every expression in the SCENE that mentions a re-evaluates as it moves — a control written inside one graph drives a curve in another beside it. name: is what it is called in front of the reader — rich text, so Frequency $b$ sets its own maths — and without one the row is labelled with the parameter itself. The current value is derived: prose cites it with {{#a.value}}, which reaches the control by its node id, so a control the prose cites is written with one (slider#spread:s(…)). The plain case, and the one to reach for: a quantity that moves continuously, so every value between the ends is one the reader can stop at. over: binds it to a dataset column instead, so its range, its stops and its format come from the cells rather than being written out — a slider over a column of years is a year scrubber with nothing else said, and every mark carrying a slice: over that column reads itself against it. To have the scene drive it rather than the reader, write cue.slider; to offer a handful of choices rather than a track, selector.