I think this is working as designed, la handler is called before its parent snot , before siblings are parsed and added to parent, so naturally next_sibling_text returns empty string until the parent snot handler is called

So the best and simples solution is to do this testing in a handler for the parent

#!/usr/bin/perl --

use strict;
use warnings;

use XML::Twig;

my $xml = <<'__XML__';
<?xml version="1.0" encoding="UTF-8"?>
<root>
    <snot>the <la>snot</la> balls are made of snot
</snot>
    <snot>the <la>snot</la> bells are made of snot
</snot>
    <snot>the <la>snot</la> bowls are made of snot
</snot>
</root>
__XML__



#~ Handlers are triggered in fixed order, sorted by their type
#~ (xpath expressions first, then regexps, then level), then by
#~ whether they specify a full path (starting at the root element)
#~ or not, then by by number of steps in the expression , then
#~ number of predicates, then number of tests in predicates.
#~ Handlers where the last step does not specify a step
#~ ("foo/bar/*") are triggered after other XPath handlers. Finally
#~ "_all_" handlers are triggered last.

{
    my @snot;
    my $t = XML::Twig->new(
        twig_handlers => {
            'snot' => sub {
                warn $_->path, "\n";
                push @snot, $_->text;
                return !!1;
            },
## la , triggered before snot
            'la' => sub {
                warn $_->path, "\n";
                push @snot, [
                    $_->text ,
## doesn't contain next_sibling_text because not parsed yet, as expect
+ed
                    $_->parent->text ,
                ];
                return !!1;
            },
        },
    );
    $t->parse($xml);

    undef $t;
    use Data::Dumper();
    print Data::Dumper->new([ \@snot ])->Indent(1)->Dump;
}


__END__
/root/snot/la
/root/snot
/root/snot/la
/root/snot
/root/snot/la
/root/snot
$VAR1 = [
  [
    'snot',
    'the snot'
  ],
  'the snot balls are made of snot
',
  [
    'snot',
    'the snot'
  ],
  'the snot bells are made of snot
',
  [
    'snot',
    'the snot'
  ],
  'the snot bowls are made of snot
'
];
[download]