Why can't a class method call a protected instance method, as in the 
following example?

class Foo
  def Foo.class_meth foo
    foo.prot_meth
  end
  
  protected
  def prot_meth
    puts 'foo'
  end
end

Foo.class_meth Foo.new 
# ==> NameError: protected method `prot_meth' called ...