Source

File: wp-includes/class-wp-customize-setting.php

protected function set_root_value( $value ) {
		$id_base = $this->id_data['base'];
		if ( 'option' === $this->type ) {
			$autoload = true;
			if ( isset( self::$aggregated_multidimensionals[ $this->type ][ $this->id_data['base'] ]['autoload'] ) ) {
				$autoload = self::$aggregated_multidimensionals[ $this->type ][ $this->id_data['base'] ]['autoload'];
			}
			return update_option( $id_base, $value, $autoload );
		} elseif ( 'theme_mod' === $this->type ) {
			set_theme_mod( $id_base, $value );
			return true;
		} else {
			/*
			 * Any WP_Customize_Setting subclass implementing aggregate multidimensional
			 * will need to override this method to obtain the data from the appropriate
			 * location.
			 */
			return false;
		}
	}