Empty on Android, iOS and the web, which have no REAPER installation to borrow from.
Controls only what a plugin list presents; every entry stays in the catalog.
searchPaths(paths, alsoUseDefaults): the locations searched in addition to, or instead of, the platform's conventional ones. A rescan is needed afterwards (AppModel.refreshFastScannedPlugins).
searchPaths(paths, alsoUseDefaults)