A plugin can hook into the core of PWG by registering event handlers with PWG. An event handler is nothing more than a function that PWG will call.

register_event_handler('delete_user', 'my_action_on_delete_user');

In this case, 'delete_user' is the name of the event to which the plugin will hook. PWG will automatically call your function when a user is deleted.

PWG will trigger actions and events. The only difference between actions and events from a coding perspective is that you are required to return a value in the case of an event (this return value will be used later by PWG).

An example of action is 'delete_user' or 'delete_elements'. Your plugin can take any required actions when a user is deleted by registering an event handler for 'delete_user'. While handling actions you are not expected to directly return a value that will be used by PWG, but you can modify any global variable in order to change the general behaviour.

An example of event is 'render_user_comment_content'. PWG will give in input the raw content of a comment, you can modify it at your will (for example allow bbcode or add smilies) and return the value:

register_event_handler('render_user_comment_content', 'my_function');
function my_function($content)
{
  $content = str_replace(':)', 'http://example.com/icon_smile.gif', $content);
  return $content; //<-- NOTE: this is how you return the value to PWG 
}

While nobody will impose a coding standard here are some things you should consider:

PHP does not allow several function names to be defined at the same time. Keep in mind that your plugin will need to work with other plugins activated, as well as the core of PWG, so please avoid function names such as 'send', 'delete', 'delete_user'… You have two options:

A. Prefix function names with something unique: 'download_multi_delete_user', 'download_multi_delete_elements', etc…

B. Use objects and classes

// class EXAMPLE
  class MyClass
  {
    function on_delete_user() { ... }
  }
  add_event_handler('delete_user', array('MyClass', 'on_delete_user') );
// object EXAMPLE
  class MyClass
  {
    function on_delete_user() { ... }
  }
  $myObj = new MyClass();
  add_event_handler('delete_user', array(&$myObj, 'on_delete_user') );

When PWG loads the plugins, it will include every main.inc.php. Don't put in your main.inc.php 3000 lines of code just to add a page on the administration menu. Split you main.inc.php in several files and feel free to add include_once inside functions defined in main.inc.php as much as you want.

function my_add()
{
  global $template;
  $url_to_me = get_root_url().'plugins/my_plugin/';
  // add a stylesheet
  $template->assign_block_vars('head_element', array (
    'CONTENT' => '<link rel="stylesheet" type="text/css" href="'.$url_to_me.'style.css">'
    ));
  // add a javascript
  $template->assign_block_vars('head_element', array (
    'CONTENT' => '<script type="text/javascript" src="'.$url_to_me.'my_script.js"></script>'
    ));
}
 
add_event_handler('loc_end_page_header', 'my_add' );