The constraint in §8.4.2 #extent-region that tts:extent shall be present on all region elements makes no statement about the default region, which of course has no corresponding region element. It may be worth clarifying that the constraint does not in and of itself require that regionelements are present in the document instance, and that the constraint in any case would not apply to the default region where the equivalent extent would be "100% 100%" by definition.
The constraint in §8.4.2
#extent-regionthattts:extentshall be present on allregionelements makes no statement about the default region, which of course has no correspondingregionelement. It may be worth clarifying that the constraint does not in and of itself require thatregionelements are present in the document instance, and that the constraint in any case would not apply to the default region where the equivalent extent would be"100% 100%"by definition.