With optgroups mock data
attributes:
$drupal: true
options:
- type: option
value: a
label: Value a
- type: option
value: b
label: Value b
- type: optgroup
label: Group a
options:
- type: option
value: a1
label: Value a1
- type: option
value: a2
label: Value a2
- type: optgroup
label: Group b
options:
- type: option
value: b1
label: Value b1
- type: option
value: b2
label: Value b2