detecting nodes in xml

Question

for example, we have this xml:

<p>[TAG]
    <span>foo 1</span>
    <span>foo 2</span>
   [/TAG]
    <span>bar 1</span>
    <span>bar 2</span>
</p>

how can i detect <span>-tags between words [TAG] and [/TAG] ("foo 1" and "foo 2" in this case)?

UPD. for example i need to change nodeValue of each span between [TAG] and [/TAG]

Answer 1

Assuming that you only have one set of [TAG]..[/TAG] per node (as in, if your document has two sets they're within separate <p> elements or whatever), and that they're always siblings:

You can use preceding-sibling and following-sibling to select only elements which are preceded by a [TAG] text node and followed by a [/TAG] text node:

//span[preceding-sibling::text()[normalize-space(.) = "[TAG]"]][following-sibling::text()[normalize-space(.) = "[/TAG]"]]

A full PHP example:

$doc = new DOMDocument();
$doc->loadHTMLFile('test.xml');

$xpath = new DOMXPath($doc);

foreach ($xpath->query('//span[preceding-sibling::text()[normalize-space(.) = "[TAG]"]][following-sibling::text()[normalize-space(.) = "[/TAG]"]]') as $el) {
 $el->nodeValue = 'Changed!';
}

echo $doc->saveXML();