What is the "bookmark" of my terminal when I touch the icon on my touchbar?

Question

When I tapped this:

It says:

What is that for?

Answer 1

This has annoyed me for years, but I finally figured it out. The Mac terminal has a bookmarks feature. You may have noticed a very light [ that's put at the left edge of every line that you typed on (another mysterious "feature") That [ indicates a bookmarked line. It's put there automatically because the Termial app's "Edit->Marks->Automatically Mark Prompt Lines" option is set. You can go up to the the previously bookmarked line with Cmd-Up-Arrow, and move down to the next bookmark with Cmd-Down-Arrow.

That's a pretty worthless feature until you turn "Automatically Mark Prompt Lines" off. Now, instead of bookmarking literally every command you type, a bookmark is inserted only when you press that icon on the touchbar. You can then return to that line with a Cmd-Up-Arrow.

Bookmarks are not named, and they're all deleted when you close the terminal window.