"Please consider using \A and \Z to test the entire input string."

I agree with this in principle; however, there's a subtle difference between \Z (uppercase) and \z (lowercase).

• /\A ... \z - matches the entire input string.
• /\A ... \Z - matches the entire input string except for a terminal newline, if it exists.

Here's a couple of one-liners to demonstrate this:

$ perl -E 'my $x = qq{qwerty\n}; $re = qr{\Aqwerty\Z}; say +($x =~ /$r
+e/) ? 1 : 0;'
1
$ perl -E 'my $x = qq{qwerty\n}; $re = qr{\Aqwerty\z}; say +($x =~ /$r
+e/) ? 1 : 0;'
0
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See Assertions under perlre - Regular Expressions which has:

"To match the actual end of the string and not ignore an optional trailing newline, use \z."