As geography is relative, boundaries should be "open-ended." As far as financial markets are concerned, however, membership can be defined by the time zone. The majority of East Asian countries are located within the 3-hour time band from Sydney to Bangkok. Thus, it is of little surprise that the countries in this zone constitute the core of numerous regional groups.
13  See J C Williams (2009), Heeding Deadalus: Optimal Inflation and the Zero Lower Bound, Brookings Papers on Economic Activity 2, pp 1–37; O J Blanchard, G Dell’Ariccia and P Mauro (2010), Rethinking Macroeconomic Policy, Journal of Money, Credit and Banking 42, pp 199–215.