We have an enough old but still supported website which is XHTML 1.0 Transitional now. We are going to change it to HTML 5 to add some new features in the future (microdata,
<footer> tags, etc).
At the moment, we are planning just change the doctype to
<!doctype html> and do some polishing to make our website fully compatible with HTML 5 standard. How can this doctype change affect our SERP positions and other things related to SEO?