The gv-includes tag is used in layout templates to reference or "include" a partial layout template inside of another. The contents of the included partial will be inserted inside the corresponding HTML element before the templates are executed by the governor system. But partial layouts appearances can be edited individually in the governor front app.
<!--[if IE 9]> <html lang="en" class="ie9"> <![endif]-->
<div gv-includes="head.html"></div> <!--gv-includes looks for the file name inside the 'includes' folder-->
Remember, gv-includes are shown in their own place inside the Governor app. Creating includes for big pieces of static content such as the navigation or footer areas help make it easier for users to keep track and edit in one place.