do_action( 'start_previewing_theme', WP_Customize_Manager $this )

Fires once the Customizer theme preview has started.

Parameters

Used By	Description
wp-includes/class-wp-customize-manager.php: WP_Customize_Manager::start_previewing_theme()	If the theme to be previewed isn’t the active theme, add filter callbacks to swap it out at runtime.

Version	Description
3.4.0	Introduced.

© 2003–2021 WordPress Foundation
Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/hooks/start_previewing_theme