Another output module, this one is called from an AJAX request in site.js. AJAX requests need to use $this->out('name', 'value') to add to the JSON response. They name used must be whitelisted in the setup.php file under 'allowed_output'.
This is an output modules that was assigned to the "home" page id. It outputs after the content_section_start core module, and outputs a div with "hello world" as a link to the hello world page
This is an output module assigned to the hello_world page identifier (this is done in the setup.php file). This looks for the data sent from the Hm_Handler_hello_world_page_handler module and outputs it after the content_section_start module