Extract from M-x describe-mode for debugger-mode

emacs-debugger-mode-help.txt

Debugger mode defined in ‘debug.el’:
Mode for backtrace buffers, selected in debugger.

A line starts with ‘*’ if exiting that frame will call the debugger.
Type b or u to set or remove the ‘*’.

When in debugger due to frame being exited,
use the r command to override the value
being returned from that frame.

Use M-x debug-on-entry and M-x cancel-debug-on-entry to control
which functions will enter the debugger when called.

Complete list of commands:
key             binding
---             -------

0 .. 9          digit-argument

TAB             forward-button
RET             debug-help-follow
ESC             Prefix Command
SPC             next-line
-               negative-argument
R               debugger-record-expression
b               debugger-frame
c               debugger-continue
d               debugger-step-through
e               debugger-eval-expression
h               describe-mode
j               debugger-jump
l               debugger-list-functions
q               top-level
r               debugger-return-value
u               debugger-frame-clear
v               debugger-toggle-locals
<backtab>       backward-button
<mouse-2>       push-button
<remap>         Prefix Command

C-M-i           backward-button