[
 {
  id => 'alpha', numeric => [ 0, 1 ],
  name => "Flux capacitance", units => ..., doc => ...,
  # absence of default means it's required
 },
 {
  id => 'beta', numeric => [ -100, +100 ],
  name => "Bogon density", default => 0, units => ...,
  doc => ...,
 },
]