Halliday & Matthiessen (2014: 625):
Endophoric reference means that the identity presumed by the reference item is recoverable from within the text itself – or, to be more precise, from the instantial system of meanings created as the text unfolds. As the text unfolds, speakers and listeners build up a system of meanings – this is part of the process of logogenesis… . Once a new meaning has been introduced, it becomes part of that system, and if it is the right category of thing, it can be presumed by endophoric reference.