Current base-asset oracle price, in quote units.
OptionalbookRaw orderbook mid price, absent when either side of the book is empty.
Optional where markPrice is not: mark falls back to the index price
upstream, whereas a raw mid has none.
The API sends JSON null here, but the websocket parser maps null to
undefined, so a === null check would never match.
Current collateral price, in USD.
Market object ID for the price update.
Current mark price — what positions are marked against for PnL and liquidation, as opposed to the raw index price.
Websocket payload for oracle price updates.