How to classify images inside a WordPress post?

Question

PHP

Good day everyone.

Suggest a solution to the problem. How to set a class for all images that are inside a post?

It is necessary to set the img class.

<figure class="wp-block-image size-large">
<img src="https://66.media.tumblr.com/e852a06b7e1fbf228dc52b996720c0b3/tumblr_pw9s3vrBoG1utlor0o1_1280.jpg" alt="" class="">
</figure>

You can set it manually, of course, but it is necessary that the class be assigned by default.

Answer 1

The easiest way is on the hook with a the_contentregular replacement or a regular expression, but this is if the pictures always have the same structure (for example, we know exactly what the tag will be <img src="..." class="..." ...). But in general, parsing html with regular expressions is not the brightest idea - there is a DOMDocument for this:

function add_class_to_images( $content )
{
    $document = new DOMDocument();
    libxml_use_internal_errors(true); // чтобы не ругался на семантические HTML5 теги
    $document->loadHTML( $content );
    libxml_clear_errors();

    $images = $document->getElementsByTagName( 'img' );

    /** @var \DOMElement $image */
    foreach ( $images as $image ) {
        $image->setAttribute( 
            'class', 
            $image->getAttribute( 'class' ) . ' my-new-class'
        );
    }

    return $document->saveHTML();
}
add_filter( 'the_content', 'add_class_to_images' );