ability to set a default value for a prop on a complex-list input i.e. a checkbox: true

[jzevin]

Is your feature request related to a problem? Please describe.

We need the ability to set checkbox: true on a input: checkbox in a complex-list similarly to setting options in a checkbox-group

Describe the solution you'd like

something like

_has:
  input: checkbox
    -
      checked: true

Describe alternatives you've considered

none

Additional context

n/a