#!/usr/bin/perl

use strict;
use warnings;

use Regexp::Common;

my $dur = qr /-?                           # Optional leading minus.
              P                            # Required.
              (?=[T\d])                    # Duration cannot be empty.
           (?:(?!-) $RE{num}{int} Y)?      # Non-negative integer, Y (optional)
           (?:(?!-) $RE{num}{int} M)?      # Non-negative integer, M (optional)
           (?:(?!-) $RE{num}{int} D)?      # Non-negative integer, D (optional)
           (?:T (?=\d)                     # T, must be followed by a digit.
           (?:(?!-) $RE{num}{int} H)?      # Non-negative integer, H (optional)
           (?:(?!-) $RE{num}{int} M)?      # Non-negative integer, M (optional)
           (?:(?!-) $RE{num}{decimal} S)?  # Non-negative decimal, S (optional)
           )?                              # Entire T part is optional
             /x;

while (<DATA>) {
    chomp;
    print "$_ ", /^$dur$/ ? "matches\n" : "does not match\n";
}

__DATA__
PnYnMnDTnHnMnS
-P1Y
P3Y3M3DT3H3M3S
P3M3Y3DT3H3M3S
P334Y3DT3H3M3S
PT2H
5T
PT
P5M6DT
P5M6DT9
P600T6S
P1347Y
P1347M
P1Y2MT2H
P0Y1347M
P0Y1347M0D
P-1347M
-P1347M
P1Y2MT
P1Y2M
P
PT0S
PT0.1234S