Dependent values
The following form uses the schema PagePropertiesSchema:Dependent_values.
The first field (country) is a OOUI DropdownInputWidget with items taken from the template Template:Countries.
The second field is a LookupElement with query
[[name::<country>]][[states/name::<value>~]]
where <country> is the name of the first field and <value> is the value being inserted in the input.. The requested printout is states/name that match the path properties/states/items/properties/name in the schema PagePropertiesSchema:Country. (where only relevant property names are concatenated, leaving aside properties and items that belong to the schema structure).
{{#pagepropertiesform: Dependent values
|title = Dependent values
|action = create
|edit-page =
|return-page =
|view = inline
|popup-size = medium
|css-class =
|pagename-formula =
|edit-freetext = false
|edit-categories = false
|edit-content-model = false
|default-categories = tasks
|default-content-model = json
|layout-align = top
|popup-help = true
|submit-button-text =
|layout = tabs
|submit-button-text =
|validate-button-text =
}}