In Perl is there a difference between /^/ and /^/m?

Question

The documentation for the /m option in perlre says this:

Treat string as multiple lines. That is, change "^" and "$" from matching the start or end of the string to matching the start or end of any line anywhere within the string.

But this example seems to indicate that /^/ and /^/m behave the same way. What am I misunderstanding?

use strict;
no warnings; # Ignore warning about implicit split to @_
my $x = " \n \n ";
print scalar(split /^/m, $x), scalar(split /$/m, $x), "\n";  # 33
print scalar(split /^/,  $x), scalar(split /$/,  $x), "\n";  # 31

Answer 1

Yes, /^/ is different than /^/m, but because /^/ would be useless when used with split, it (for split only) automatically becomes /^/m. This is documented in perldoc -f split.

This is the kind of surprising DWIM that would probably not be included in perl if we had to do it all over again.