[RFC] Mixed type

Hi Internals, Here is an RFC for adding a 'mixed' type to the language: https://wiki.php.net/rfc/mixed_type_v2 The RFC builds on an earlier draft by Michael Moravec. Part of the motivation for pursuing this RFC was my recent experience in upgrading an application to PHP 7.4. Being able to add types to the application made the code much easier to reason about, but there were places where I couldn't add type info due to the lack of mixed. That made it hard to see if that piece of code had been upgraded (but type info couldn't be added), or if that code still needed to be upgraded. cheers Dan Ack