Bug 156883 [Viewers] enhancements to ILazyTreeContentProvider
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
Item current = getItem(x, y);
		if (current != null) {
			Item previous = getPreviousItem(current);
			showItem(previous == null ? current : previous);
			return previous;
		}
		return null;
	}
	/**
	 * Sets the auto-expand level. The value 0 means that there is no
	 * auto-expand; 1 means that top-level elements are expanded, but not their
	 * children; 2 means that top-level elements are expanded, and their
	 * children, but not grandchildren; and so on.
	 * <p>
	 * The value <code>ALL_LEVELS</code> means that all subtrees should be
	 * expanded.
	 * </p>
	 * 
	 * @param level
	 *            non-negative level, or <code>ALL_LEVELS</code> to expand all
	 *            levels of the tree
	 */
	public void setAutoExpandLevel(int level) {
		expandToLevel = level;
	}
	/**
	 * The <code>AbstractTreeViewer</code> implementation of this method
	 * checks to ensure that the content provider is an
	 * <code>ITreeContentProvider</code>.
	 */