Return an AttributeList that is the result of merging first with second.

def merge(cls, first, second):
        """
        Return an AttributeList that is the result of merging first with second.
        """
        merged = AttributeList([], None)

        assert (isinstance(first, AttributeList))
        assert (isinstance(second, AttributeList))
        merged._contents = first._contents[:]
        merged._contents += second._contents[:]

        return merged