delegates.php

// current proposal
public function process(ServerRequestInterface $request, DelegateInterface $delegate)
{
    // ...
    return $delegate->process($request);
}

// alternative
public function process(ServerRequestInterface $request, DelegateInterface $next)
{
    // ...
    return $next($request);
}

// assuming that...
interface DelegateInterface
{
    public function __invoke(ServerRequestInterface $request);
}