Adding 'dir' attribute to all paragraphs (UNTESTED)

ParagraphDirProcessor.php

<?php

// TODO: Set your "namespace" and "use" statements here
// Also see this documentation: http://commonmark.thephpleague.com/customization/abstract-syntax-tree/#document-processor

class ParagraphDirProcessor implements DocumentProcessorInterface
{
    public function processDocument(Document $document)
    {
        $walker = $document->walker();
        while ($event = $walker->next()) {
            $node = $event->getNode();

            // Only stop at Paragraph nodes when we first encounter them
            if (!($node instanceof Paragraph) || !$event->isEntering()) {
                continue;
            }

            $node->data['attributes']['dir'] = 'rtl';
        }
    }
}