In looking at a calendar I was evaluating I noticed that the « Prev Next » links didn't have a heading to explain what they were for. This was instituted in Drupal 7 Core:
https://drupal.org/node/254940#theme-links-param

I thought I'd be able to just add it to the date-views-pager.tpl.php, but there's already a header there that just isn't being used in the Calendar:
theme/date-views-pager.tpl.php:

print $nav_title

Now I could adjust this, but ultimately whether it is invisible or not should be something that should be configurable. Not sure if it needs to be done in:
theme/theme.inc: $nav_title = theme('date_nav_title', $params);

But one should have a default title that is invisible to everyone but the screen reader users.