What does this screen do?

1. Look for the (i) beside the heading of the block you are on. Every documented section has one.
2. On a computer, rest the pointer on the mark to open the explainer. Move away to close it.
3. Press the mark, or press anywhere in the panel, and it stays open until you close it. On a phone, press it.
4. It shows three things: what this is, what you get, and good to know.
5. The last one folds after a few lines. The rest is one press away.
6. The menu down the left highlights the tab you are on. The sections inside it are the row of choices across the top of the page.
7. On a phone, both are in the panel behind Tabs on the bottom bar.
8. Press a section name to go to it. It goes into the address, so a link you copy opens on the same place.
9. If a heading has no (i), the section is not documented yet. Ask here instead, and the answer goes into the written answers.