tixHList Says: "If the -selectmode is "extended", when the user drags the mouse pointer over the list entries, all the entries under the pointer will be highlighted. The user can also make disjointed selections using <Control-ButtonPress-1>."

$mw->HList(-selectmode => 'extended', ...
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-selectmode => 'multiple' only allows for contiguous selection, via click&drag or click&shift-click.

-selectmode => 'extended' allows for all that, plus non-contiguous selection, via ctrl-click.

Here is an example that will demonstrate the differences:

#!/usr/bin/perl
use strict;
use warnings;
use Tk;
use Tk::HList;

my $mw = MainWindow->new();

my $hlist = $mw->HList(
  -itemtype   => 'text',
#  -selectmode => 'multiple',
  -selectmode => 'extended',
  -browsecmd  => \&bc,
);
my $text = $mw->Text();

my @words = qw(
  aback  abaft  abandon
  babble babies baboon
  cabal  cabana cabaret
);

$hlist->add($_, -text=>$_) foreach qw(a b c);
foreach ( @words ) {
  my $first = substr($_, 0, 1);
  $hlist->add("$first.$_", -text=>$_);
}

$hlist->pack(-side => 'top',    -fill => 'both', -expand => 1);
$text ->pack(-side => 'bottom', -fill => 'both', -expand => 1);

MainLoop;

sub bc {
  my $sel = join "\n", $hlist->infoSelection();
  $text->delete('1.0', 'end');
  $text->insert('end', $sel);
}
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Are you talking about a hash table? There is no proximity relationship among the keys of hash table, so "next to each other" would be undefined. You can use hash slices to select the values corresponding to multiple keys; e.g.

@ids{qw( Ann Bert Chuck )}
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-selectmode => 'multiple',
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See Tk-POP3-previewer for an example.