Fires immediately before partials are rendered.
Plugins may do things like call wp_enqueue_scripts() and gather a list of the scripts and styles which may get enqueued in the response.
(WP_Customize_Selective_Refresh) Selective refresh component.
(array) Placements' context data for the partials rendered in the request. The array is keyed by partial ID, with each item being an array of the placements' context data.