SkinID- Tells WSI which skin to look in for extant XML packages. This will return packages in the {root}/XmlPackages folder as well as the skin XmlPackages folder.
PackageTypePrefix- Tells WSI which package types to return a list of. Valid values are 'entity', 'product', 'notification', 'feed', 'page', and 'skin'. If left blank, all packages will be returned.
If no SkinID is specified, WSI will use the site's default skin.