A my declares the listed variables to be local (lexically) to the enclosing block, file, or eval. If more than one variable is listed, the list must be placed in parentheses.
The exact semantics and interface of TYPE and ATTRS are still evolving. TYPE may be a bareword, a constant declared with use constant, or __PACKAGE__. It is currently bound to the use of the fields pragma, and attributes are handled using the attributes pragma, or starting from Perl 5.8.0 also via the Attribute::Handlers module. See "Private Variables via my()" in perlsub for details, and fields, attributes, and Attribute::Handlers.
Note that with a parenthesised list, undef can be used as a dummy placeholder, for example to skip assignment of initial values:
my ( undef, $min, $hour ) = localtime;