Documentation on session refers to rules from a topic that does not exist any more?

From manual page: https://php.net/intro.session

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The documentation says "Serialize handlers (php and php_binary) inherit register_globals limitations." But as I understand the "register_globals" feature/topic/documentation does not exist any more. I think that documentation section on rules for keys names could be done in a more clear and explicit manner e.g. using bullet list of things that are not allowed. Also it is not clear if these rules apply only "root" level entries in $_SESSION or also for nested data. Because all of these issues I am not sure if I see here the complete list of rules, or perhaps there is something more under "inheregister_globals limitations" topic, that I cannot find.