What defines a 'Guru's biography' according to this text, and what distinguishes it from other spiritual knowledge texts?

Chapter 0 defines a Guru's biography as a reliable and true book that is distinct from general spiritual knowledge texts. Its specific purpose is to describe the Guru's incarnation, their life through childhood, youth, and old age, their wonderful plays or 'Leelas,' and their incomparable miracles and works. While other texts might focus purely on worldly and spiritual knowledge, a Guru's biography centers on the life and divine actions of the Guru. Studying such a text is considered a high form of Guru service, especially for devotees who regard the Guru as their ultimate guide to salvation.