Halliday & Matthiessen (2014: 389):
Within this logical structure there may be ‘sub-modification’: that is, internal bracketing … . Sub-modification may have the effect of disturbing the natural order of elements in the group; this accounts for additional items occurring before the Deictic, as in almost the last buttercup (rather than the almost last buttercup), such a bright moon (rather than a such bright moon), and also for displaced elements, as in not so very difficult a task (instead of a not so very difficult task).