Common protocol for Java elements that must be opened before they can be navigated or modified. Opening a textual element (such as a compilation unit) involves opening a buffer on its contents. While open, any changes to the buffer can be reflected in the element's structure; see {@link #isConsistent} and {@link #makeConsistent(IProgressMonitor)}.
To reduce complexity in clients, elements are automatically opened by the Java model as element properties are accessed. The Java model maintains an LRU cache of open elements, and automatically closes elements as they are swapped out of the cache to make room for other elements. Elements with unsaved changes are never removed from the cache, and thus, if the client maintains many open elements with unsaved changes, the LRU cache can grow in size (in this case the cache is not bounded). However, as elements are saved, the cache will shrink back to its original bounded size.
To open an element, all openable parent elements must be open. The Java model automatically opens parent elements, as it automatically opens elements. Opening an element may provide access to direct children and other descendants, but does not automatically open any descendents which are themselves {@link IOpenable}. For example, opening a compilation unit provides access to all its constituent elements, but opening a package fragment does not open all compilation units in the package fragment.
@noimplement This interface is not intended to be implemented by clients.