Sample: Using `WP_HTML_Tag_Processor` that is introduced WordPress 6.2.0

use-WP_HTML_Tag_Processor.php

<?php

/**
 * `WP_HTML_Tag_Processor` Modifies attributes in an HTML document for tags matching a query.
 */

$html = '<span><img src="hello.webp" alt="hello"></span>';

// Create an instance
$tags = new WP_HTML_Tag_Processor( $html );

// Seek next tags
$tags->get_tag();  // => NULL

$tags->next_tag();
$tags->get_tag();  // => 'SPAN'

// Handle attributes
$tags->set_attribute( 'class', 'myclass' );
$tags->get_attribute( 'class' );  // => 'myclass'
$tags->remove_attribute( 'class' );

// Handle class
$tags->add_class( 'is-active' );
$tags->get_attribute( 'class' );
$tags->remove_class( 'class' );

// Return modified html
echo $tags->get_updated_html();
// or
echo (string) $tags;

// Seek the next tag
$tags->next_tag(['tag_name' => 'IMG']);
$tags->get_tag();  // => 'IMG'

The official reference:

• WP_HTML_Tag_Processor | Class | WordPress Developer Resources

See also:

• A New HTML API | "What's New in WordPress 6.2 - Kinsta®"
• WordPress/wordpress-develop#3920