Creator class attribute for Expert Commentary (Challenging Concepts)
Where Chapters have a contributor classified as providing Expert Commentary, use attribute class="expertcommentator" on the creator element.
Example
<creatorGroup>
<creator class="author" invertedForm="Myat, Aung"><forenames>Myat</forenames><surname>Aung</surname>
</creator>
<creator class="expertcommentator" invertedForm="Redwood, Simon" role="Professor"><forenames>Simon</forenames><surname>Redwood</surname>
</creator>
</creatorGroup>