Yes!

Although it is not literal perl. The first argument "\&hook" is a reference to the subroutine "hook".

The second argument is optional, and thus enclosed in [ and ] characters, and similarly the last argument is optional.

So you could call it in three ways:

# just one argument.
$q = CGI->new(\&hook);

# two arguments.
$q = CGI->new(\&hook ,$data  );

# all three - party time!
$q = CGI->new(\&hook ,$data, $use_tempfile);
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Under Unix-like systems there is a convention that optional arguments are enclosed in "[" and "]" characters. For a simple example of that try readng "man ls" which has the following output:

    ls [OPTION]... [FILE]...
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