silverstripe-blog/code/extensions/BlogCommentExtension.php

<?php

/**
 * Adds Blog specific behaviour to Comment.
 */
class BlogCommentExtension extends DataExtension {
	/**
	 * Extra CSS classes for styling different comment types.
	 *
	 * @return string
	 */
	public function getExtraClass() {
		$blogPost = $this->owner->getParent();

		if($blogPost instanceof BlogPost) {
			if($blogPost->isAuthor($this->owner->Author())) {
				return 'author-comment';
			}
		}

		return '';
	}
}