is a variable defined in `
C source code
Its value is
- This variable may be risky if used as a file-local variable.
Function to call to invoke debugger.
If due to frame exit, args are `exit' and the value being returned;
this function's value will be returned instead of that.
If due to error, args are `error' and a list of the args to `signal'.
If due to `apply' or `funcall' entry, one arg, `lambda'.
If due to `eval' entry, one arg, t.