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/LibrariesWorkbookPage.java
private void editElementEntry(CPListElement elem) {
		CPListElement[] res= null;
		
		switch (elem.getEntryKind()) {
		case IClasspathEntry.CPE_CONTAINER:
			res= openContainerSelectionDialog(elem);
			break;
		case IClasspathEntry.CPE_LIBRARY:
			IResource resource= elem.getResource();
			if (resource == null) {
				res= openExtJarFileDialog(elem);
			} else if (resource.getType() == IResource.FOLDER) {
				if (resource.exists()) {
					res= openClassFolderDialog(elem);
				} else {
					res= openNewClassFolderDialog(elem);
				} 
			} else if (resource.getType() == IResource.FILE) {
				res= openJarFileDialog(elem);			
			}
			break;
		case IClasspathEntry.CPE_VARIABLE:
			res= openVariableSelectionDialog(elem);
			break;
		}
		if (res != null && res.length > 0) {
			fLibrariesList.replaceElement(elem, res[0]);
		}