Find two tags sequentially

<h2>t1</h2>
<strong>s1</strong>
</hr>
<h2>t2</h2>
<p><strong>s2</strong></p>
<strong>s3</strong>
<strong>s4</strong>
<h2>t3</h2>
<strong>s5</strong>

'h2' tags are followed by unknown number of 'strong' tags and 'p' tags, some times a 'strong' is embeded in 'p'. Sometimes, other tags, such as 'hr', exist. Is there a way to retrieve all 'h2', and each 'h2' is followed by the first 'strong' after the 'h2'. For example, for the above code, I would like to get:

t1
s1
t2
s2
t3
s5

I tried to get all 'h2' in one array, and all 'strong' in another, but I could not find which 'strong' is the first one that is following an 'h2'.

You can use the following ways:

include_once 'simple_html_dom.php';


$nodes = str_get_html('<h2>t1</h2>
<strong>s1</strong>
</hr>
<h2>t2</h2>
<p><strong>s2</strong></p>
<strong>s3</strong>
<strong>s4</strong>
<h2>t3</h2>
<strong>s5</strong>')->nodes;

Get the sequential list

$list = [];
foreach($nodes[0]->children as $child) {
  if($child->tag == 'h2' || $child->tag == 'strong') {
    $list[] = $child->innertext;
  }
}

result

array (size=7)
  0 => string 't1' (length=2)
  1 => string 's1' (length=2)
  2 => string 't2' (length=2)
  3 => string 's3' (length=2)
  4 => string 's4' (length=2)
  5 => string 't3' (length=2)
  6 => string 's5' (length=2)

Get nested list

$nested = [];
$a = -1;
foreach($nodes[0]->children as $child) {
    if($child->tag == 'h2') {
      $a++;
      $nested[$a]['value'] = $child->innertext;
    } elseif($child->tag == 'strong') {
      $nested[$a]['children'][] = $child->innertext;
    }
}

Result

array (size=3)
  0 => 
    array (size=2)
      'value' => string 't1' (length=2)
      'children' => 
        array (size=1)
          0 => string 's1' (length=2)
  1 => 
    array (size=2)
      'value' => string 't2' (length=2)
      'children' => 
        array (size=2)
          0 => string 's3' (length=2)
          1 => string 's4' (length=2)
  2 => 
    array (size=2)
      'value' => string 't3' (length=2)
      'children' => 
        array (size=1)
          0 => string 's5' (length=2)