Until now the composer had two ways out: schedule it, or publish it now. Both of them require the post to be finished. Anything half-written, a good first line or a thread you meant to come back to after lunch, had nowhere to go, and closing the composer threw it away.
Posts can now be saved as drafts.
What gets kept
Everything, as it stands. The text on each account, including where they have diverged from one another, the media, any poll, and which accounts you had selected. Reopening a draft puts you back where you left it rather than at an approximation of it.
A draft doesn't have to have anything in it. Start one, save it, and it will be waiting. An empty post is a perfectly good note to self.
Where they go
Drafts land in the Drafts column on the planner we shipped on Monday, and in the schedule's sidebar. Open one to keep writing, and schedule or publish it from there when it is ready. Nothing about a draft is different from any other post except that it hasn't gone anywhere yet.
Closing asks first
If you close the composer with unsaved content, it now asks: save as draft, discard, or cancel and carry on writing. Losing work should take a deliberate click, not a stray one.