Bug 123786 Following bug 109980, the compliance 6.0 should be added to the compiler's compliance list.
If the JRE/JDK used is a 1.6/6.0 VM, then the compliance 6.0 should be available. Compliance 1.6 implies source level 1.6 and target level 1.6.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/JavaProjectWizardFirstPage.java
private String getDefaultJVMName() {
			return JavaRuntime.getDefaultVMInstall().getName();
		}
		private String getDefaultJVMLabel() {
			return Messages.format(NewWizardMessages.JavaProjectWizardFirstPage_JREGroup_default_compliance, getDefaultJVMName());
		}
		public void update(Observable o, Object arg) {
			updateEnableState();
		}
		private void updateEnableState() {
			final boolean detect= fDetectGroup.mustDetect();
			fUseDefaultJRE.setEnabled(!detect);
			fUseProjectJRE.setEnabled(!detect);
			fJRECombo.setEnabled(!detect && fUseProjectJRE.isSelected());
			fPreferenceLink.setEnabled(!detect);
			fGroup.setEnabled(!detect);
		}
		
		/* (non-Javadoc)
		 * @see org.eclipse.swt.events.SelectionListener#widgetSelected(org.eclipse.swt.events.SelectionEvent)
		 */
		public void widgetSelected(SelectionEvent e) {
			widgetDefaultSelected(e);
		}
		/* (non-Javadoc)
		 * @see org.eclipse.swt.events.SelectionListener#widgetDefaultSelected(org.eclipse.swt.events.SelectionEvent)
		 */
		public void widgetDefaultSelected(SelectionEvent e) {
			String jreID= BuildPathSupport.JRE_PREF_PAGE_ID;
			String complianceId= CompliancePreferencePage.PREF_ID;