Bug 28510 java build path inconsistency [build path]
20021216 select rt.jar in the package explorer open properties it allows you to set the javadoc location but for source attachment you are sent somewhere else it's inconsistent - on the java build path they both look sort of the same (they sit under the same node in the tree)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/CPListElement.java
public Object[] getChildren(boolean hideOutputFolder) {
		if (fEntryKind == IClasspathEntry.CPE_CONTAINER) {
			try {
				IClasspathContainer container= JavaCore.getClasspathContainer(fPath, fProject);
				IClasspathEntry[] entries= container.getClasspathEntries();
				CPListElement[] elements= new CPListElement[entries.length];
				for (int i= 0; i < elements.length; i++) {
					elements[i]= createFromExisting(entries[i], fProject);
					elements[i].setParentContainer(this);
				}
				return elements;
			} catch (JavaModelException e) {
				return new Object[0];
			}
		}
		if (hideOutputFolder && fEntryKind == IClasspathEntry.CPE_SOURCE) {
			return new Object[] { fAttributes.get(EXCLUSION) };
		}
		return fAttributes.values().toArray();
	}
	
	private void setParentContainer(CPListElement element) {
		fParentContainer= element;
	}
	
	public CPListElement getParentContainer() {
		return fParentContainer;
	}