Elementor: experiments and markup-changing features

For developers shipping a companion plugin / theme that adds widgets, dynamic tags, or frontend CSS/JS on top of Elementor. Elementor ships "experiments" (feature flags) under core/experiments/manager.php. Most are cosmetic, but two Performance experiments change the rendered HTML and are default-ON on new installs, so a modern addon must handle them or it silently breaks on a large share of sites.

Read this first — you cannot assume the state

Experiment state is per-site and three-valued (Default / Active / Inactive), and the effective default differs between fresh and upgraded installs. Never hardcode an assumption; detect at runtime:

if ( \Elementor\Plugin::$instance->experiments->is_feature_active( 'e_optimized_markup' ) ) {
    // adapt markup
}

Verified: Experiments\Manager::is_feature_active( $name, $check_dependencies = false ) at core/experiments/manager.php:257; actual state resolves to the user's explicit state unless it's Default, then the feature's default (manager.php get_feature_actual_state).

The two markup-changing experiments (both release_status => STABLE, tag "Performance", new_site.default_active => true) — verified manager.php:312-381: