Y: make a callback plugin for Drupal-7 / YAD7

Create a YAML configuration file example.yaml and put these contents in it:

routing:
  !name :
    menu: !menucallback
      page callback: examplecallback

In that same directory, make a callback PHP file called example.inc and define your examplecallback function. For example,

<?php
function examplecallback() {
  // do something here
}