XenForo comes with 2 default rendering options for forum nodes, which you can make use of in your add-on.
First option, rendering them as a HTML <select>:
You can do this by setting:
Edit Format: PHP Callback
Format Parameters: XenForo_Option_NodeChooser::renderSelect
The second option renders them as a HTML radio:
You can do this by setting:
Edit Format: PHP Callback
Format Parameters: XenForo_Option_NodeChooser::renderRadio
You can (of course) set your own rendering options by putting your own callback.
UPDATE: You can also do this with usergroups by using the following callbacks:
Select - XenForo_Option_UserGroupChooser::renderSelect
Radio - XenForo_Option_UserGroupChooser::renderRadio
First option, rendering them as a HTML <select>:
You can do this by setting:
Edit Format: PHP Callback
Format Parameters: XenForo_Option_NodeChooser::renderSelect
The second option renders them as a HTML radio:
You can do this by setting:
Edit Format: PHP Callback
Format Parameters: XenForo_Option_NodeChooser::renderRadio
You can (of course) set your own rendering options by putting your own callback.
UPDATE: You can also do this with usergroups by using the following callbacks:
Select - XenForo_Option_UserGroupChooser::renderSelect
Radio - XenForo_Option_UserGroupChooser::renderRadio