Rationale:
1. The principle of pingbacks is based on articles. Pingbacks are a special kind of comments and the article being 'pinged-back' has to be identifiable (which they're not on archive pages and the like).
2. WP only registers a ping if it can identify the article which is supposed to have been 'pung'. See: https://developer.wordpress.org/reference/classes/wp_xmlrpc_server/pingback_ping/
3. Pingbacks, like comments, can be disabled on a per article basis.
Therefore, having the pingback url auto-discovery header in place, only makes sense on singular pages where pings are open.
Even with WordPress’ commitment to backwards compatibility, we should
probably not bank on private functions being around for ever, and tying
our functionality to it.
This will go old school and do a version check to provide compatibility
with older versions of WordPress. Again, this is only temporary until
4.3 is out.
See #644.
Fixes#636.
Set up author data for the author template immediately, rather than
waiting for the first the_post() call.
This removes the need to call the_post() and rewind_posts() in an
author template to print information about the author.
Fixes#346.
* Update PHPDoc.
* Add periods to the end of comment sentences.
* Limit line length to 80 chars.
* Use C++-style PHP comments only for function and file documentation.