Debugger mode is derived from Backtrace mode, which is also used to show
backtraces by Edebug and ERT. (*note Edebug::, and *note the ERT manual:
The backtrace buffer shows you the functions that are executing and
their argument values. When a backtrace buffer is created, it shows
each stack frame on one, possibly very long, line. (A stack frame is
the place where the Lisp interpreter records information about a
particular invocation of a function.) The most recently called function
will be at the top.
In a backtrace you can specify a stack frame by moving point to a
line describing that frame. The frame whose line point is on is
considered the “current frame”.
If a function name is underlined, that means Emacs knows where its
source code is located. You can click with the mouse on that name, or
move to it and type , to visit the source code. You can also type
while point is on any name of a function or variable which is not
underlined, to see help information for that symbol in a help buffer, if
any exists. The ‘xref-find-definitions’ command, bound to , can
also be used on any identifier in a backtrace (*note (emacs)Looking Up
In backtraces, the tails of long lists and the ends of long strings,
vectors or structures, as well as objects which are deeply nested, will
be printed as underlined “...”. You can click with the mouse on a
“...”, or type while point is on it, to show the part of the
object that was hidden. To control how much abbreviation is done,
Here is a list of commands for navigating and viewing backtraces:
Toggle the display of local variables of the current stack frame.
Move to the beginning of the frame, or to the beginning of the
Move to the beginning of the next frame.
Add line breaks and indentation to the top-level Lisp form at point
to make it more readable.
Collapse the top-level Lisp form at point back to a single line.
Toggle ‘print-circle’ for the frame at point.
Toggle ‘print-gensym’ for the frame at point.
Expand all the forms abbreviated with “...” in the frame at point.