When using WordPress, it is likely that anyone who has ever opened source code will see the file xmlrpc.php located in the root directory source. XML-RPC is a script used in WordPress since the previous version but since version 3.5 it has been turned on by default.
XML-RPC is a protocol that connects to remote WordPress web sites using XML to exchange data. Currently supported APIs of CMS such as WordPress API, Blogger API, Movable API, Pingback...
