With a captured spren, you may begin designing a proper fabrial. It is a closely guarded secret of artifabrians that spren, when trapped, respond to different types of metals in different ways. A wire housing for the fabrial, called a “cage,” is essential to controlling the device. —Lecture on fabrial mechanics presented by Navani Kholin to the coalition of monarchs, Urithiru, Jesevan, 1175
