tag_search_example.php

<?php
// search all <span> tags from a post.
$processor = new \\WP_HTML_Tag_Processor( $content );
$processor->next_tag( [ 'tag_name' => 'span' ] ); // search by tag 
$processor->next_tag( [ 'class_name' => 'fullwidth' ] ); // search by class name 
$processor->next_tag( [ 'class_name' => 'fullwidth', 'tag_name' => 'img' ] ); // search by class name and by tag name at the same time.