[WordPress] Adding Custom WordPress Image Attributes

00-the-content.php

<?php

private function addImageAttributes($content)
{

  $content  = mb_convert_encoding($content, 'HTML-ENTITIES', "UTF-8");
  $document = new \DOMDocument();

  libxml_use_internal_errors(true);
  $document->loadHTML(utf8_decode($content));

  $images = $document->getElementsByTagName('img');
  foreach ($images as $image) {
      $image->setAttribute('data-example', 'true');
  }

  return $document->saveHTML();
}

This isn't really designed to be used in a child theme - instead, it's meant for an object-oriented plugin so you'd have to refactor it a bit if you wanted it to work in the context of a theme.

Namely, you'd need to:

• remove private function the function
• pass the value of the string or the content into the function that you want it to parse
• make sure DOMDocument is available in your installation of PHP
• then echo the code that's returned from this function

It's a lot looking at this way but hopefully it gives you a starting point!