Halliday & Matthiessen (2014: 625-6):
Exophora and endophora are different directions of pointing – either to referents in the environment outside the text, or to referents introduced in the text itself before or after the reference expression. But how does this reference expression achieve the effect of ‘pointing’? All such expressions have in common the fact that they presuppose referents; but they differ with respect to whether what is presupposed is the same referent (co-reference) or another referent of the same class (comparative reference): see Table 9-9.
