[Pre-RFC] Improve language coherence for the behaviour of offsets and containers

Hello internals, I would like to get some initial feedback on an RFC I've been working on for the last 5–6 months. The RFC attempts to explain, and most importantly, improve the semantics around $container[$offset] as PHP is currently widely inconsistent. The RFC is about six thousands words, so I would recommend a cup of tea/coffee before starting to read it. The main things which are still in flux is the naming of the new interfaces and methods, the phrasing of error messages, and the behaviour around using null as a container. Those are generally indicated with a TODO comment. Of note is that I will also be going on holiday for 3 weeks from the 19th of March, so ideally most of the feedback would come during that time frame so that I can finalize the RFC after my holiday. RFC: https://github.com/Girgias/php-rfcs/blob/master/container-offset-behaviour.md Best regards, Gina P. Banyard