topic-tags template

Where is the topic-tags page template specified?

It seems that the page template for most of the pages is specified in class-shortcodes-php.  I ended up having to change the page template here because the functionality to change page templates seems to have disappeared from the plugin.  In general, this works.  However, when I go to a particular topic tag, such that I am in the topic-tag subdirectory, it reverts to page.php.  I can't find where the page template is specified for this so that I can change it.