I'm following the tutorial's "Making error": reproduced in the screenshot below. The manufactured error does not open the Backtrace window as it should. The same page says "It is possible to prevent Emacs entering the debugger in cases like this. [...] in the echo area and look like this:
Symbol's function definition is void: this
". And that is indeed what I get. Thus my question: how to switch on the backtrace feature?
In your mode line, [...] suggests you have an existing backtrace is running, you need to quit this one in order to trigger a new backtrace, you can do this by C-x b *Backtrace* and q.
If there is something in the mode line you don't understand, you can use mouse hover to see the tooltip. For example, if you hover [ or ], it will say something like "Recursive edit, type C-M-c to get out". (emacs) Recursive Edit is a feature that allow users continue to use Emacs without quit the current command, in this debugging case, you can use continue to use Emacs as usual while you're debugging Emacs itself. To quit one Recursive edit, you can use C-M-c (exit-recursive-edit, one level) or C-] (abort-recursive-edit, all levels) or M-x top-level (actually q in the end of the first paragraph runs top-level).
