wp-includes/class-wp-customize-widgets.php:1940Begins keeping track of the current sidebar being rendered.
$indexint|string public function start_dynamic_sidebar( $index ) { array_unshift( $this->current_dynamic_sidebar_id_stack, $index ); if ( ! isset( $this->sidebar_instance_count[ $index ] ) ) { $this->sidebar_instance_count[ $index ] = 0; } $this->sidebar_instance_count[ $index ] += 1; if ( ! $this->manager->selective_refresh->is_render_partials_request() ) { printf( "\n<!--dynamic_sidebar_before:%s:%d-->\n", esc_html( $index ), (int) $this->sidebar_instance_count[ $index ] ); } }Introduced in 4.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-customize-widgets.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.