WordPress at a glance
action is not described

setup_theme action-hook . WP 2.6.0

Fires before the theme is loaded.

Usage

add_action( 'setup_theme', 'action_function_name_387' );
function action_function_name_387(){
	// action...
}

Changelog

Since 2.6.0 Introduced.

Where the hook is called

In file: /wp-settings.php
setup_theme
wp-settings.php 492
do_action( 'setup_theme' );

Where in WP core the hook is used WordPress

wp-includes/class-wp-customize-manager.php 366
add_action( 'setup_theme', array( $this, 'setup_theme' ) );
wp-includes/default-filters.php 496
add_action( 'setup_theme', 'create_initial_theme_features', 0 );