The knobs join a layout::seeded seed, so a changed starting value,
option list or range starts every setting over, and a renamed knob
no longer fails. new() refuses no knobs, twin names and a number
outside its range. Controls are keyed by knob name. The test presses
keys without a refresh, so only a notify redraws, and walks the
switch twice, the slider twice and a pick the owner takes away.
tooling::Playground lays a preview beside its knobs, each a switch, a
choice or a number that edits one property; the preview redraws from
the settings, which fail on a name or kind the knobs lack. The gallery
app is the ComponentGallery; its page 43 shows both.
ZacharyZhang-NY