Perl Protocol Declaration

Intro

All parsed code must begin with use vX; It is a directive to the interpreter which tells it how to parse the following code.

Allowed ways to specify the protocol

The following pragmas are required by perl 7 before any code is allowed to be parsed. Comments and whitespace are permissible. -x applies.

use v5;
use v7;

# This is a placeholder. Open for bikeshed.
use current; # Tell the parser to use the major of the current binary. 

Mixed protocols

The following is allowed but won't technically work on perl 5:

use v7;
sub foo ($bar) {
    ...;
}

use v5;

package foo;
sub bar ($@) {
    ...;
}

1;

How it works

At this time (5 and 7) it really only affects $^H, %^H, and $^WARNINGS but this may change at a future date.