OptionalactionThe named action the key fires instead of typing - backspace/delete/left/
right/confirm/cancel, the same vocabulary a physical key is bound to. A
key with an action types nothing.
the key's own caption
Optionalspanrow units wide; a space bar is wide, an ordinary key is 1. Default 1
OptionaltextWhat the key types through core.Input's onText. Defaults to label, so an
ordinary letter key is just { label: 'A' }; a wider gap or an accented glyph
can say { label: 'a', text: 'à' }`.
one key: what it is labelled, what it types, or which action it fires