The essence of these purses is that they form a single whole multisignature wallet! The purse asset is allocated to a separate array and is not stored there for long, until the transaction is completed
Bitshare wallet for inactive funds. This wallet is optional, under the trader's full control, and is for storing funds. Any funds to be traded must be moved first to a multisignature wallet for active funds.
Multisignature wallet for active funds. This is the wallet used for trading. The trader and the DEVX signatures have the same weight, so that neither can withdraw funds from the wallet without the other's approval. This prevents the mid-trade withdrawal of funds by either the trader or DEVX.