I've rewritten my managesieve patch using plugin api and I've found a few issues:

1. Templates from plugin directory. I've commited patch from Roland Liebl

and it's possible now, but... images path is hardcoded to "plugins/plugin_name/...", and will not work if someone will change plugins_dir.

2. include_script() includes script after rcmail variable initialization.

That's ok, but there's a one situation when it's a problem.

For 'html' output I must write: $this->rc->output->add_script(sprintf("rcmail.managesieve_updatelist('%s', '%s', %d);", isset($new) ? 'add' : 'update', $this->form['name'], $fid), 'foot'); instead of more unified form: $this->rc->output->command('managesieve_updatelist', isset($new) ? 'add' : 'update', $this->form['name'], $fid);

3. Localization folder name should be constant for all plugins (hardcoded in api).

Creating plugins translator will be simpler then.