WPF has introduced virtualized controls in past releases;
however there was never a standardized way for an automation client to interact
with a virtualized control. Two control patterns, ItemsContainerPattern and
VirtualizedItemPattern, have been added in WPF 4 to support access and interact
with virtualized elements. ItemsContainerPattern is used to access the
virtualized controls & find virtualized items and VirtualizedItemPattern is
used to realize virtualized items.