They just need to register to the PLUGIN_USAGE_DATA event, and then to add
either a simple string, or an array of key / value. For example:

    function register(Doku_Event_Handler $controller) {
      $controller->register_hook('PLUGIN_USAGE_DATA', 'AFTER', $this, 'usage_data');
    }

    function usage_data(&$event){
      $event->data['my_plugin_name'] = 'my usage data';

      //or: $event->data['my_plugin_name'] = array ('k1' => 'v1', 'k2' => 'v2');
    }

removed </a>

It is helpful if the pipe is still inserted by the linkwizard when there
is no title. This increases usability for beginners.

This reverts commit 3940c519 as
discussed in #1082.

When the picker button is near the border of the screen, then an opening panel of picker buttons can go over the screen edge. That's not convenient. So we should add a check in a `function pickerToggle()` and shift picker buttons position if needed.

The user properties (login, real name, etc) where not properly escaped
in the user manager's edit form. This allowed a XSS attack on the
superuser by registered users.

Thanks to Filippo Cavallarin from www.segment.technology for discovering
this bug.

Added file-in-use reference to page

Since we cannot effectively filter for groups and have to work with
incremental prefetching, the ``last`` button is mostly broken/buggy.
Hence it is disabled in this usecase.