YARD doc - how to document a class type focusing on its parent class

Suppose I have the following

class AbstractClass; end
class ConcreteClass1 < AbstractClass; end
class ConcreteClass2 < AbstractClass; end

How do I document a return value that returns a class instance of a class that inherits AbstractClass (either ConcreteClass1 or ConcreteClass2) ? I want to focus on the fact that the return value can be either ConcreteClass1 or ConcreteClass2 but what matters is that they are all kind_of(AbstractClass)

I was thinking of something like this, is it the good approach ?

# Class MyClassFactory implements the factory pattern for selecting the appropriate class for xxx
def MyClassFactory
  # @return [? < AbstractClass] an instance of a class inheriting AbstractClass
  def create_instance(*args)
     if cond?
       ConcreteClass1
     else
       ConcreteClass2
     end.new(*args)
  end
end

Now suppose my method returns the class itself, and not a class instance, would this be the good approach ?

def MyClassFactory
  # @return [? <= AbstractClass] the class to be used
  def select_class
     if cond?
       ConcreteClass1
     else
       ConcreteClass2
     end
  end
end

It's sufficient to write

# @return [AbstractClass]

The reader should assume that Liskov substitution may apply. The Abstract prefix (as well as an @abstract tag) will also communicate this clearly, and the resulting documentation will list ConcreteClass1 and ConcreteClass2 under the "Direct Known Subclasses" of AbstractClass.

As for returning a class, the YARD creator's recommendation is to use Class<AbstractClass>.