Require entity for custom service

Development
1

I’m pretty sure I’m missing something obvious here - but when I register a new service for a custom platform, how do I make the UX prompt for an entity (as, for example “turn_on” does for light)

I’d expect this to do it, but…

NOON_SCENE_SCHEMA = vol.Schema({
    vol.Optional(ATTR_ENTITY_ID): cv.entity_ids,
})
hass.services.register("switch", "set_scene", handle_set_scene, schema=NOON_SCENE_SCHEMA)