A simple element is a UI element that shares an IAccessible object with other elements and relies on that IAccessible object (typically its parent) to expose its properties. To differentiate between the elements sharing an IAccessible object, the server assigns a unique, positive child identifier to each simple element. This assignment is done on a per-instance-of-interface basis, so the IDs must be unique within that context. Many implementations assign these IDs sequentially, beginning with 1. This scheme does not allow simple elements to have children of their own. Simple elements are also known as children.
To be uniquely identified and exposed, a simple element requires an IAccessible object and child ID. Therefore, when communicating with an IAccessible object, the clients must supply the appropriate child ID. A special identifier, CHILDID_SELF, can be used to refer to the accessible object itself, instead of one of its children.
The IAccessible object shared among simple elements often corresponds to a common parent object in the user interface. For example, system list boxes expose an accessible object for the overall list box and simple elements for each list box item. In this case, the IAccessible object for the list box is also the parent or container of the list items.
For more information about accessible objects, see Accessible Objects.