Some authors issue open licences for their works to anyone who wishes to use the works. Popular free licences are the Creative Commons licence and the GNU licence for free documentation. The requirements are minimal. It is often enough to name the author. But even though the requirements are minimal, they must still be met. Otherwise, there would be a contractual infringement and costs may be incurred even if it involved a free licence. It is also worth ensuring that the licensor really owns the rights they are granting under the free licence. If they are not the author or if they have previously transferred the rights, the user/licensee can be made liable for damages because good faith is not protected.