my @DELIMS = (qw( _ @ ));
...
... /[@DELIM]/ ...
[download]

If the default value of  $" is unchanged, the array  @DELIMS will be interpolated into the regex character class with an extraneous space character, which is then a valid part of the class: a bug waiting to happen. Locally set  $" to the empty string or, better yet, use join to form the char class string.

>perl -wMstrict -le
"my @DELIMS = (qw( _ @ ));
 ;;
 my $rx = qr{[@DELIMS]};
 print $rx;
 ;;
 { local $\" = '';  $rx = qr{[@DELIMS]}; }
 print $rx;
 ;;
 my $cc = join '', @DELIMS;
 $rx = qr{[$cc]};
 print $rx;
"
(?^:[_ @])
(?^:[_@])
(?^:[_@])
[download]

Do not multiply bugs without necessity!