Prev

var label = $0 ?? $label ?? "<< Prev";

var pages = [ xml.num(id) foreach var id in wiki.tree(page.parents[0].path)['//@pageid'] ];
var current = list.indexof(pages, page.id);
var prev;
if(current > 0) {
    let prev = wiki.getpage(pages[current - 1]).uri;
}
if(prev) {
    <a href=(prev ? prev : '#')> label </a>
} else {
    <span> label </span>
}