Is there a reason not to do the following?
<div comment="start display area">
<!--Start display area-->
You should use data attributes. Data attributes are designed exactly for what you're intending to do:
HTML5 is designed with extensibility in mind for data that should be associated with a particular element but need not have any defined meaning. data-* attributes allow us to store extra information on standard, semantic HTML elements without other hacks such as non-standard attributes, extra properties on DOM, or setUserData.
Your div would look like:
<div data-comment="start display area">