We've just deployed an inline preview capability. Just press Preview and a re-sizable panel will appear beneath your code.
You can expand it into its own browser tab with a click in the preview header.
Read more (well, not a lot more) in the documentation.
This is the latest, but by no means the last, feature to come off the production line. We're going to be announcing three new ones in the next few days, so keep your eyes peeled.
