# in IDE:
# open the `core/units/users/users_event_handler.php` file for editing
# in the `\UsersEventHandler::SetCustomQuery` method after calling the parent method add `$b = $a + 1;`
# save changes
# in Admin Console
# go to the {nav User Management > Administrators} section
# confirm, that an `Undefined variable: a` notice appears in Debugger
# go to the {nav Logs & Reports > System Log} section
# confirm, that record for the `Undefined variable: a` notice was created
# open the record for the `Undefined variable: a` notice for viewing/editing
# confirm, that the backtrace looks visually the same as in other system log records
# click on the `Function:` link in any of the backtrace records
# confirm, that:
* the `Arguments:` text is shown above function/method arguments
* the `Toggle Code...` link is shown below function/method arguments
# click on the `Toggle Code...` link once
# confirm, that:
* a highlighted code fragment appears
* each line in a the code fragment has a line number, that corresponds to the line number in the associated file
* line number associated with the trace is marked with the `>>> ` sign