wp-includes/class-wp-customize-manager.php:4683Gets messenger channel.
string public function get_messenger_channel() { return $this->messenger_channel; }Introduced in 4.7.0. 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-manager.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.