如何交叉引用锚标签？

Question

XHTML:

<root>
<a href="1#fn1" class="fn-ref" id="s9781473910270.i11"><sup>1</sup></a>
<p>some text<a href="1#fnref1" id="s9781473910270.i237">↩</a></p>
</root>

From the above sample, if href of both anchor are same (like 1#fn1 and 1#fnref1 ) then have to exchange their ID's as their href and have to wrap the anchor tag(which has fnref in their href in it) with <span class="label-fn"> then need to set class="ref-fn-ref" for that anchor tag.

Expected output:

<root>
<a href="#s9781473910270.i237" class="fn-ref" id="s9781473910270.i11"><sup>1</sup>
</a>
<p>sometext<span class="label-fn"><a href="#s9781473910270.i11" class="ref-fn-ref" 
id="s9781473910270.i237">↩</a></span></p>
</root>

I have tried so far,

libxml_use_internal_errors(true);
$dom = new DOMDocument;
$dom->loadHTMLFile("sample.xhtml", LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
$xp = new DOMXPath($dom);
$xp->registerNamespace("php", "http://php.net/xpath");
$className="fn-ref";
$anchor1 = $xp->query("//[contains(@class, '$className')]");
//????

I stucked in between, I don't know how to get the array of another anchor tags matched with anchor1 array.

Answer 1

Figured out myself to get my output.

$dom = new DOMDocument;
$dom->loadHTML($html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
$xp = new DOMXPath($dom);
$xp->registerNamespace("php", "http://php.net/xpath");
$a1 = $xp->query("//*[contains(@class, 'fn-ref')]");
$a2 = $xp->query("//*[contains(@href, '#fnref')]");

foreach($a1 as $a1v) {
    $id1=$a1v->getAttribute('id');
    preg_match("/([\\d]+)#fn([\\d+])/s",$a1v->getAttribute('href'),$m1);
    $href1=$m1[1]."#fnref".$m1[2];  
    foreach($a2 as $a2v) {
    if($a2v->getAttribute('href')===$href1){
        $id2=$a2v->getAttribute('id');
        $a2v->setAttribute('class','ref-fn-ref');
        $a2v->setAttribute('href',"#".$id1);
        $a1v->setAttribute('href',"#".$id2);
        break;
    }
}
}
$r=$dom->saveXML();