Your second question is about canvas tags also. There is a difference between the canvas's bind and the normal Tk::bind. The canvas's bind will let you bind to a tag. If you look at each canvas item's creation, you will see it is given a tag(s). This is the basis of the canvas's power, because you can do all sorts of trickery with addtag and deltag to change an item's tags dynamically. So you can do things like setup a callback when a mouse enters any item with a certain tag. Like this:

#!/usr/bin/perl
use Tk;

my $mw = MainWindow->new();
$mw->geometry("600x400+100+100");
$canvas = $mw->Canvas(width => 600, height => 400)->pack();
$canvas->Tk::bind("<Button-1>", [ \&print_xy, Ev('x'), Ev('y') ]);

# This draws half of an oval
$oval = $canvas->createOval(100,100,200,250,-fill => 'white',-tags => 
+"blue");

$canvas->Tk::bind("<Button-3>", sub {$canvas->itemconfigure($oval,-fil
+l => "red")});

$canvas->bind('blue', '<Enter>', 
            sub { $canvas->itemconfigure("blue", -fill => "blue"); } )
+;
    # sub {exit});
# When the mouse is not over, color it black.
$canvas->bind("blue", "<Leave>",
         sub { $canvas->itemconfigure("blue", -fill => "black"); });

#$tw->tagBind('tag','<Enter>',sub{$overtag=1});

MainLoop;

sub print_xy {
  print "@_\n";
  my ($canv, $x, $y) = @_;
  print "(x,y) = ", $canv->canvasx($x), ", ", $canv->canvasy($y), "\n"
+;
}
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