In perlboot, an intro to OO in Perl, it is discussed in The extra parameter of method invocation.
Update: To answer your updated question, the package name or blessed object are passed in a method invocation whenever you use the The Arrow Operator to invoke a package method. So Node->new() will pass "Node" and new(), Node::new() or $code_ref->() would not.
It's the first thing perlobj says about methods
A Method is Simply a Subroutine
Unlike say C++, Perl doesn't provide any special syntax for method definition. (It does provide a little syntax for method invocation though. More on that later.) A method expects its first argument to be the object (reference) or package (string) it is being invoked on.