The page you are looking at is being generated dynamically by MaskPHP.
If you would like to edit this page you'll find it located at:
module/helloworld/view/index/index.php
The corresponding controller for this page is found at:
module/helloworld/controller/index.php
The Debug component provides several tools to help you debug PHP code.
?debug_token=true
If you are exploring MaskPHP for the very first time, you should start by reading the User Guide.