如果项目具有一个或多个子元素，则xpath不匹配

Question

I have a method that looks like this:

function braces(DOMElement $node){
    $path   = $node->getNodePath();
    $xpath = new DOMXPath($node->ownerDocument);
    $nodes = $xpath->query($path . '[*=(contains(., "{{") and contains(., "}}"))]');

    var_dump($nodes);
}

I have created the following two test cases:

Test Case 1

$dom = new DOMDocument();
$dom->loadHTML('<div data-id="{{cat}}">
    <a href="http://google.com">Google</a>
</div>',LIBXML_HTML_NODEFDTD | LIBXML_HTML_NOIMPLIED);

braces($dom->documentElement);

The var_dump() on this one does not find the attribute with {{ and }}.

Here is test case 1's resulting output:

object(DOMNodeList)#4 (1) {
  ["length"]=>
  int(0)
}

Test Case 2

$dom = new DOMDocument();
$dom->loadHTML('<div data-id="{{cat}}"></div>',LIBXML_HTML_NODEFDTD | LIBXML_HTML_NOIMPLIED);

braces($dom->documentElement);

When removing the child a element, the var_dump() now can find the attribute with {{ and }}.

Here is test case 2's resulting output:

object(DOMNodeList)#3 (1) {
  ["length"]=>
  int(1)
}

So, my question is why can't it find the value when the item has children?

Answer 1

Take another look at your predicate

*=(contains(., "{{") and contains(., "}}"))

This is an equality comparison with two operands. The right-hand operand is a boolean (A and B is always boolean). XPath 1.0, therefore, forces the left-hand operand to be a boolean as well. "*" selects the children of the context node; boolean(*) is true if that node-set is non-empty, that is, if the context node has one or more children.

So your equality comparison is true if either (a) the node has children and contains braces, or (b) the node has no children and does not contain braces.

What do I mean by contains here? The expression contains(., 'x') is true if the string value of the node contains 'x' as a substring. The string value of a node derives from the children/descendants of the node; it takes no account of attributes. Because it ignores attributes, your contains() test is false in both cases, so the predicate as a whole is true only if the left-hand operand is also false, that is, if the node has no children.