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

Question

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-->
<li>Home</li>
<!--sub-items-->
<ul class="sub active">
<li>Barn</li>
<li>Activities</li>
<ul class="sub active">
<li>News</li>
<li>Movements</li>
<li>Reviews</li>
<li>About Us</li>
<li>Terms of Use</li>
</ul>
</ul>
<li>Events</li>
<ul class="sub">
<li>Overview</li>
<li>Farming</li>
<li>Practises</li>
<li>Links</li>
<ul class="sub">
<li>Another Farm</li>
<li>24m</li>
</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.

Answer 1

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-->
<li>Home</li>
<!--sub-items-->
<ul class="sub active">
<li>Barn</li>
<li>Activities</li>
<ul class="sub active">
<li>News</li>
<li>Movements</li>
<li>Reviews</li>
<li>About Us</li>
<li>Terms of Use</li>
</ul>
</ul>
<li>Events</li>
<ul class="sub">
<li>Overview</li>
<li>Farming</li>
<li>Practises</li>
<li>Links</li>
<ul class="sub">
<li>Another Farm</li>
<li>24m</li>
</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);
}