On Windows 10, the generic.xaml file for UWP apps is available for reference in the C:\Program Files (x86)\Windows Kits\10\DesignTime\CommonConfiguration\Neutral\UAP\10.0.x.0\Generic folder, where x refers to the installed SDKs' versions. Within this file, I've come across the ListViewItemExpanded and GridViewItemExpanded styles. These are included in addition to the default styles for ListViewItem and GridViewItem.
Neither ListViewItem nor GridViewItem has an IsExpanded property, nor do their docs mention "expand", so when and how are these styles applied?