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

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-->
    <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.

@Alejandro how do I know what version of XPath I am running? Also if it was not supported surely it would just return false right? — Scott Anderson
– Scott Anderson, Commented Apr 18, 2019 at 13:51
If the function is not defined for your execution context, the XPath engine should report an error. From within XPath execution context there is no way to know the supported language version. If an XPath 2.0 function fails, then you have an XPath 1.0 engine. — Alejandro
– Alejandro, Commented Apr 18, 2019 at 14:06
It says at php.net/manual/en/domxpath.query.php that if the query is invalid it will return false, but if I use an unsupported function are you saying that php will actually throw an error? Because I have tried lower-case() and it didn't throw an error about it, just returned 0 matches — Scott Anderson
– Scott Anderson, Commented Apr 18, 2019 at 14:42

miken32 · Accepted Answer · 2019-04-21 17:33:44Z

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-->
    <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);
}

edited Apr 21, 2019 at 17:33

answered Apr 20, 2019 at 23:54

miken32

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3 Comments

Scott Anderson Over a year ago

thankyou, inspecting the error log would have been useful, I had libxml_surpress_errors on because it was writing to document

Scott Anderson Over a year ago

It does successfully match now and currently it works without the xpath namespace declaration which is even better!

miken32 Over a year ago

Well there are no namespaces involved anywhere here, so I can't see why you'd need them, but glad you got it working.

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