use warnings;
use 5.028;
use experimental 'regex_sets';
use open qw/:std :utf8/;
use charnames ':full';

my $PERL_IDENT_RE =
	qr/ (?[ ( \p{Word} & \p{XID_Start} ) + [_] ])
	    (?[ ( \p{Word} & \p{XID_Continue} ) ]) *    /x;

for my $c ( 0x2211, 0x03A3, 0x222B, 0x0283 ) {
	printf "%s U+%04X %s %s\n", chr($c), $c, charnames::viacode($c),
		chr($c) =~ /\A$PERL_IDENT_RE\z/ ? "matches" : "doesn't match";
}