Working on a new default theme is always an opportunity to improve coreCore Core is the set of software required to run WordPress. The Core Development Team builds WordPress.’s Theme APIs too. With the release of Twenty Fifteen there are quite a few improvements that made it in:

Archive Template Tags

Theme authors get to use four new functions to use in their archive templates:

get_the_archive_title() and the_archive_title() for returning/displaying the title of the current term, date, post type, post format, or author archive.

and for returning/displaying the title of the current term, date, post type, post format, or author archive. get_the_archive_description() and the_archive_description() for returning/displaying the description associated with the current term archive.

They are especially handy when a theme doesn’t have dedicated templates for taxonomyTaxonomy A taxonomy is a way to group things together. In WordPress, some common taxonomies are category, link, tag, or post format. https://codex.wordpress.org/Taxonomies#Default_Taxonomies. or date archives, but can essentially be used in all archive templates. The description functions only display term descriptions, since no other archive type really offers descriptions.

Worked on in #21995 and then introduced in r30223.

Navigation Template Tags

Core has provided template tags for links between posts and pages of posts for a long time. Now theme authors can resort to higher-level template tags to display an entire navigation snippet. If you’ve built your themes off of recent default themes, or created child themes from them, these should look very familiar. As a heads up: Since default themes have been developed in HTML5 for five years now, there is no HTML4 version of these tags.

get_the_post_navigation() and the_post_navigation() for navigation to the next and previous post.

and for navigation to the next and previous post. get_the_posts_navigation() and the_posts_navigation() for navigation to the next and previous page of posts.

and for navigation to the next and previous page of posts. get_the_posts_pagination() and the_posts_pagination() for paginated navigation between pages of posts. (Updated for 4.1 RC1, see this post)

All functions use the same wrapping markup with semantic class names, so it’s easy to style them in one go. The navigation functions accept custom link texts and screen-reader-texts, in case the defaults are not applicable. The pagination functions even accept all arguments that paginate_links() does, too! (Except for the 'type' argument, we need that to be plain so the template tagtag A directory in Subversion. WordPress uses tags to store a single snapshot of a version (3.6, 3.6.1, etc.), the common convention of tags in version control systems. (Not to be confused with post tags.) doesn’t break 😉 )

Worked on in #29808, introduced in r30065, improved in r30457.

Also in 4.1:

Theme Support for Title Tags

I’ve written about title tags before and will refer to that post for more information about the groundbreaking changes that happened here.

Page Template Body Classes

They got a minor update that simplifies those class names and allows theme authors to target folders of page templates. With this /page-templates/full-width.php will produce page-template , page-template-page-templates , page-template-full-width and page-template-page-templatesfull-width-php . Worked on in #23470 and then introduced in r30100.