marked by C<b> and those with actions by C<a>. The line that's
about to be executed is marked by C<< ==> >>.
+Please be aware that code in debugger listings may not look the same
+as your original source code. Line directives and external source
+filters can alter the code before Perl sees it, causing code to move
+from its original positions or take on entirely different forms.
+
=item Frame listing
When the C<frame> option is set, the debugger would print entered (and