With a lot of talk happening around the PSR-7 HTTP request/response proposal and PSR-4 being the last "official" standard to be posted, some people are wondering what happened to PSR-5 and 6. Phil Sturgeon, a previous member of the PHP-FIG, has posted some clarification to how the PSR process works and where those seemingly missing PSR numbers are at.

The last PSR from the FIG to be sent out into the world, to be used by whoever felt like using it, was PSR-4: Autoloader. Now people are starting to hear about PSR-7, and they’re starting to “lolphp”, wondering what has happened to PSR-5 and PSR-6. [...] This is not like The Neverending Muppet Debate of PHP 6 v PHP 7, despite it being the first though to pop into many peoples heads. Instead, this is down to the Workflow Bylaw I put into place last year.

He goes on to talk about the current workflow stages and how, unlike systems in other languages, the PHP-FIG's process gives proposals a PSR number even before they're published and accepted. He also briefly talks about PSR "nicknames", naming to differentiate between similar proposals and how, despite the need for these names, they're just reference points for conversations more than anything.