I'd like to clarify something please… What would be the point to say that there MUST be a space (so from one to many) between type and name, whereas it's not possible to have 0 space, as it would be syntactically invalid?

Do we expect PSR to explicitly redefine the PHP rules?

If not, my feeling would be that the intention was to require one single space after the property type.

syntactically this is still correct/working... (PHP is impressive inconsistent in this case)

class test
{
    public FlightHeader$flight_header;
    public Carbon$flight_date;
    public BookingNumber$booking_number;
    public ?string$booking_class;
}

thats why i see a difference between "must be a space" and "must be one space"

and PSR makes a difference between 'one space' and 'a space'

4.5 Method and Function Arguments
In the argument list, there MUST NOT be a space before each comma, and there MUST be one space after each comma.

in this example is explicit one space defined

syntactically this is still correct/working... (PHP is impressive inconsistent in this case)

class test
{
    public FlightHeader$flight_header;
    public Carbon$flight_date;
    public BookingNumber$booking_number;
    public ?string$booking_class;
}

thats why i see a difference between "must be a space" and "must be one space"

WOW! 😱 Sorry for this, I should have tested it before answering…