You need findnodes if you want to return multiple results

for my $attr_node (
    reverse
    $xc->findnodes('//post:entry/post:category/@term')
) {
    my $attr_val = $attr_node->getValue();
    ...
}
[download]

Or maybe you want

for my $entry_node ( reverse $xc->findnodes('//post:entry') ) {
    for my $attr_node ( $xc->findnodes('post:category/@term', $entry_n
+ode) ) {
        my $attr_val = $attr_node->getValue();
        ...
    }
    ...
}
[download]