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Why the DB::DB is called twice for:
print "@{[ (caller(0))[0..2] ]}\n";
but only one for this:
print sb();
A: It is called once for caller(0) and second for whole line.
It is called once for each statement at line, maybe.


+
use should have args. and the caller called from DB:: namespace should set @DB::args
at compile time 'caller' also does not fill @DB::args
BEGIN {
	print caller, @DB::args
}
A: Try, to ensure the DB::args used after the call ot caller
BEGIN {
	@caller =  caller
	print @caller, @DB::args
}



How 'the first non-DB piece of code' is calculated for the 'eval'?



#BUG? I can ${ '!@#$' } =  3, but can not my ${ '!@#$' }


BUG?
The localization of $DB::single works fine, but the reference to it does not work:
	{
		$DB::single =  7; my $x =  \$DB::single;
		print "Before: ". \$DB::single ." <<$x $$x\n";
		local $DB::single =  0;
		print "After: ". \$DB::single ." <<$x $$x\n";
	}

The output:
Before: SCALAR(0x10f8310) <<SCALAR(0x10f8310) 7
After: SCALAR(0x110cbc8) <<SCALAR(0x10f8310) 0

Where as works fine:
	{
		$DB::z =  7; my $x =  \$DB::z;
		print "Before: ". \$DB::z ." <<$x $$x\n";
		local $DB::z =  0;
		print "After: ". \$DB::z ." <<$x $$x\n";
	}
The output:
Before: SCALAR(0x134d398) <<SCALAR(0x134d398) 7
After: SCALAR(0x1239bc8) <<SCALAR(0x134d398) 7

We see that in *first* example the new variable is created: The new address of $DB::single is SCALAR(0x110cbc8)
but when assigning to $DB::single the value by old reference (SCALAR(0x10f8310) changed too.
In *second* example we see that addressing works in same manner, but value 7 is preserved as expected.

Why the value of $DB::single is not preserved?

	# my $y =  \$DB::single;
	# # Can not use weaken. See error at 'reports/readline' file
	# use Scalar::Util 'weaken';
	# weaken $y;
	# Because of $DB::single magic we can not access to old value by reference
	# The localization is broken if we save a reference to $DB::single
	# {
	# 	my $x =  $DB::single;
	# 	print "Before: ". \$DB::single ." <<$DB::single $x >$y $$y\n"; # $$x == 0
	# 	local $DB::single =  $DB::single +1;
	# 	print "After: ". \$DB::single ." <<$DB::single $x >$y $$y\n";  # $$x == 1, not 0
	# }
	# print "OUT: ". \$DB::single ." <<$DB::single - $x - $$x >$y\n";

	# {
	# 	print "BEFORE: $DB::single\n";
	# 	local $DB::single =  7;
	# 	print "AFTER $DB::single\n";
	# }
	# print "OUT $DB::single\n";

	# BUG: The perl goes tracing if you uncomment this
	# { local $DB::trace =  1; }
	# # But it shows us the value 0 but internally it is 1
	# die $DB::trace   if $DB::trace != 0;



sub sub {
	...
	# BUG: without +0 the localized value is broken
	local $DB::single =  ($DB::single & 2) ? 0 : $DB::single+0;


Breakpoint does not work for this when hash key is initialized
  b  x64:   my $hash = $c->stash->{'mojo.content'} ||= {};

#TODO: $X=(condition)

The debugger do not single step into sub called from string



Notice strange file:line
POP  FRAME <<<< l:0 b:0:0 e:1 s:1 t:1  --  Apache::DB::handler@1
    /home/kes/perl_lib/lib/perl5/x86_64-linux-gnu-thread-multi/Apache/DB.pm:77 }

	else {
		if (ref $r) {
		$SIG{INT} = \&DB::catch;
		$r->register_cleanup(sub {
			$SIG{INT} = \&DB::ApacheSIGINT();
		});
		}
	}

    print "HERE: " .$DB::single; #line 77
    DB::state( 'trace', 1 );
    $DB::single = 1;
    print "HERE: A" .$DB::single;


  print "DONE\n";