Halliday & Matthiessen (2014: 373):
In addition to the Deictic element we have just discussed, there may be a second Deictic element in the nominal group, one which adds further to the identification of the subset in question. We will refer to these as post-Deictic or Deictic₂.
The post–Deictic identifies a subset of the class of ‘thing’ by referring to its fame or familiarity, its status in the text, or its similarity/dissimilarity to some other designated subset.