Emacs normally displays an error message when an error is signaled and
not handled with condition-case. While Edebug is active and
executing instrumented code, it normally responds to all unhandled
errors. You can customize this with the options edebug-on-error
and edebug-on-quit; see Edebug Options.
When Edebug responds to an error, it shows the last stop point encountered before the error. This may be the location of a call to a function which was not instrumented, and within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable reference. In that case, you might want to display a full backtrace (see Miscellaneous Edebug Commands).
If you change debug-on-error or debug-on-quit while
Edebug is active, these changes will be forgotten when Edebug becomes
inactive. Furthermore, during Edebug’s recursive edit, these variables
are bound to the values they had outside of Edebug.