PHP DOMXPath->query()/->evaluate() not matching inner text

I am currently trying to create a pure PHP menu traversal system - it's because I'm doing an impromptu project for some people but they want as little JS as possible (i.e: none) and ideally pure PHP.

I have a menu which looks like this:

ul {
  list-style-type: none;
}

nav > ul.sidebar-list ul.sub {
  display: none;
}

nav > ul.sidebar-list ul.sub.active {
  display: block;
}

<nav class="sidebar" aria-labelledby="primary-navigation">
  <ul class="sidebar-list">

    <!--each element has a sub-menu which is initially hidden by css when the page is loaded. Via php the appropriate path the current page and top-level links will be visible only-->
    <a href="#"><li>Home</li></a>
    <!--sub-items-->
    <ul class="sub active">
      <a href="#"><li>Barn</li></a>
      <a href="#"><li>Activities</li></a>
      <ul class="sub active">
        <a href="#"><li>News</li></a>
        <a href="#"><li>Movements</li></a>
        <a href="#"><li>Reviews</li></a>
        <a href="#"><li>About Us</li></a>
        <a href="#"><li>Terms of Use</li></a>
      </ul>
    </ul>
    <a href="#"><li>Events</li></a>
    <ul class="sub">
      <a href="#"><li>Overview</li></a>
      <a href="#"><li>Farming</li></a>
      <a href="#"><li>Practises</li></a>
      <a href="#"><li>Links</li></a>
      <ul class="sub">
        <a href="#"><li>Another Farm</li></a>
        <a href="#"><li>24m</li></a>
      </ul>
    </ul>
  </ul>
</nav>

In order to attempt to match the title inner-text of the page to a menu-item innertext (probably not the best way of doing things but I'm still learning php) I run:

$menu = new DOMDocument();
assert($menu->loadHTMLFile($menu_path), "Loading nav.html (menu file) failed");
//show content to log of the html document
error_log("HTML file: \n\n".$menu->textContent);

//set up a query to find an element matching the title string found
$xpath = new DOMXPath($menu);

$menu_query = "//a/li[matches(text(), '$title_text', 'i')]";
$elements = $xpath->query($menu_query);
error_log($elements ? ("Result of xpath query is: ".print_r($elements, TRUE)): "The xpath query for searching the menu is incorrect and will not find you anything!\ntype of return: ".gettype($elements));

I get the correct return at: https://www.freeformatter.com/xpath-tester.html but in the script I don't. I have tried many different combinations of the text matching such as: //x:a/x:li[lower-case(text())='$title_text'] but always an empty node list.

Solution

PHP uses XPath 1.0. matches is an XPath 2.0 function, so you would have seen warnings in your error log if you were looking for them.

PHP Warning:  DOMXPath::query(): xmlXPathCompOpEval: function matches not found in php shell code on line 1
PHP Stack trace:
PHP   1. {main}() php shell code:0
PHP   2. DOMXPath->query() php shell code:1

A simple case-sensitive match can be done with an equality check.

$title_text = "Farming";
$menu_query = "//a/li[. = '$title_text']";

But the case-insensitive search involves translating the characters from upper to lower case:

$title_text = "FaRmInG";
$title_text = strtolower($title_text);
$menu_query = "//a/li[translate(., 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz') = '$title_text']";

In either case we end up with a NodeList that can be iterated through:

$html = <<< HTML
<nav class="sidebar" aria-labelledby="primary-navigation">
  <ul class="sidebar-list">

    <!--each element has a sub-menu which is initially hidden by css when the page is loaded. Via php the appropriate path the current page and top-level links will be visible only-->
    <a href="#"><li>Home</li></a>
    <!--sub-items-->
    <ul class="sub active">
      <a href="#"><li>Barn</li></a>
      <a href="#"><li>Activities</li></a>
      <ul class="sub active">
        <a href="#"><li>News</li></a>
        <a href="#"><li>Movements</li></a>
        <a href="#"><li>Reviews</li></a>
        <a href="#"><li>About Us</li></a>
        <a href="#"><li>Terms of Use</li></a>
      </ul>
    </ul>
    <a href="#"><li>Events</li></a>
    <ul class="sub">
      <a href="#"><li>Overview</li></a>
      <a href="#"><li>Farming</li></a>
      <a href="#"><li>Practises</li></a>
      <a href="#"><li>Links</li></a>
      <ul class="sub">
        <a href="#"><li>Another Farm</li></a>
        <a href="#"><li>24m</li></a>
      </ul>
    </ul>
  </ul>
</nav>
HTML;
$menu = new DOMDocument();
$menu->loadHTML($html);
$xpath = new DOMXPath($menu);
$elements = $xpath->query($menu_query);
foreach ($elements as $element) {
    print_r($element);
}