# in IDE:
# open the `modules/custom/units/widgets/widget_eh.php` file for editing
# in the `\WidgetEventHandler::SetCustomQuery` method after calling the parent method add `$b = $a + 1;`
# save changes
# in Admin Console
# go to the {nav Custom > Widgets} 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 ALL `Function:` links 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 in `Function: NParser->ParseBlock in widget_list.php on line 28` backtrace line (the line, that uses the code from the Custom module)
# click on the `Toggle Code...` link once
# confirm, that:
* a highlighted code fragment appears
* each line in 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