This comment: https://tracker.moodle.org/browse/MDL-48947?focusedCommentId=372193&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-372193 - has prompted me to think about ARIA roles ones more, so is: https://github.com/moodle/moodle/blob/MOODLE_29_STABLE/theme/bootstrapbase/layout/columns2.php#L69 a 'region' (http://www.w3.org/TR/wai-aria/roles#region) and if so, where would the label come from?
Is there a checker for ARIA roles where theme designers can check their mark-up? I've not checked recently, but wave.webaim.org has been good for colour checking etc.