[NTG-context] setupregister/placeregister

Hello, The criterium key in setupregister (so placeregister, placeindex, ...) takes the following values: criterium local text current previous all section all: places all entries of the document section: (part, chapter, section, ...) places entries associated with that structure element. Can someone explain local, text, current, previous for their scope and perhaps subtle differences are not entirely obvious to me. Thank you Alan