Days ago, I started one. Some kind of posting accident occurred, maybe user error, and what I'd written disappeared. What's tricky about captions is that your typing starts wherever the cursor is. That's no surprise, but the cursor lands at the lower right corner of a posted photo and is very hard to see. Now I know to hit Return twice after a photo if I want to say something there. The harder part is typing above the first photo in a post. How to get the cursor back up there isn't transparent. It's easier to type before inserting the photo, or else use Return before inserting the photo to make a space to type in later.
There! Now you have a first draft.