wp-includes/class-wp-xmlrpc-server.php:258Tests XMLRPC API by saying, "Hello!" to client.
string public function sayHello() { return 'Hello!'; }Introduced in 1.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-xmlrpc-server.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.