Supporting assets and liabilities (needed for OpenEconomy.org.au)

@pudo I get you. I see “type” as a per line thing too. I also realised this issue this a while back in relation to BDP here. OSDP, by inheriting this from BDP, currently expects “type” conformity in a set. We should discuss that here though, and leave this thread to specific discussion of assets and liabilities :). [LINK]