Превратить HTML в массив PHP

 $doc = new \DOMDocument();
      $doc->loadHTML($html);

      $figure = $doc->getElementsByTagName("figure"); // DOMNodeList Object

      //Craete array to add all DOMElement value
      $figures = array();
      $i= 0;
      foreach($figure as $item) { // DOMElement Object

        $figures[$i]['class']= $item->getAttribute('class');
        //DOMElement::getElementsByTagName— Returns html tag
        $img = $item->getElementsByTagName('img')[0];

        if ($img){
            //DOMElement::getAttribute — Returns value of attribute
            $figures[$i]['img']['src'] = $img->getAttribute('src');

            $figures[$i]['img']['alt'] = $img->getAttribute('alt');
            $figures[$i]['img']['class'] = $img->getAttribute('class');
        }
        //textContent - use to get the text of tag
        if ($item->getElementsByTagName('figcaption')[0]){
            $figures[$i]['figcaption'] = $item->getElementsByTagName('figcaption')[0]->textContent;
        }

        $i++;
      }

      echo "<pre>";
      print_r($figures);
      echo "</pre>";

Вот код, который должен привести вас туда, где вы хотите быть. Я добавил комментарии, где я чувствовал, что они будут полезны:

<?php

$htmlString = 'Here is some <a href = "#">text</a> which I do not need to extract but then there are <figure class = "class-one"><img src = "/example.jpg" alt = "example alt" class = "some-image-class"><figcaption>example caption</figcaption></figure>And another one (and many more)<figure class = "class-one some-other-class"><img src = "/example2.jpg" alt = "example2 alt"></figure>';

//Create a new DOM document
$dom = new DOMDocument;

//Parse the HTML.
@$dom->loadHTML($htmlString);

//Create new XP
$xp = new DOMXpath($dom);

//Create empty figures array that will hold all of our parsed HTML data
$figures = array();

//Get all <figure> elements
$figureElements = $xp->query('//figure');

//Create number variable to keep track of our $figures array index
$figureCount = 0;

//Loop through each <figure> element
foreach ($figureElements as $figureElement) {
    $figures[$figureCount]["class"] = trim($figureElement->getAttribute('class'));
    $figures[$figureCount]["img"]["src"] = $xp->query('//img', $figureElement)->item($figureCount)->getAttribute('src');
    $figures[$figureCount]["img"]["alt"] = $xp->query('//img', $figureElement)->item($figureCount)->getAttribute('alt');

    //Check that an img class exists, otherwise set the value to null. If we don't do this PHP will throw a NOTICE.
    if (boolval($xp->evaluate('//img', $figureElement)->item($figureCount))) {
        $figures[$figureCount]["img"]["class"] = $xp->query('//img', $figureElement)->item($figureCount)->getAttribute('class');
    } else {
        $figures[$figureCount]["img"]["class"] = null;
    }

    //Check that a <figcaption> element exists, otherwise set the value to null
    if (boolval($xp->evaluate('//figcaption', $figureElement)->item($figureCount))) {
        $figures[$figureCount]["figcaption"] = $xp->query('//figcaption', $figureElement)->item($figureCount)->nodeValue;
    } else {
        $figures[$figureCount]["figcaption"] = null;
    }

    //Increment our $figureCount so that we know we can create a new array index.
    $figureCount++;
}

print_r($figures);
?>