if (fEnvironment != null)
if (fIsSealed)
	private void addPosition(LinkedPosition position) throws BadLocationException {		Assert.isNotNull(position);		// don't add positions after it is installed.		if (fEnvironment != null)			throw new IllegalStateException("cannot add positions after the group is added to an environment"); //$NON-NLS-1$		if (!fPositions.contains(position)) {			enforceDisjoint(position);			enforceEqualContent(position);			fPositions.add(position);			fHasCustomIteration |= position.getSequenceNumber() != LinkedPositionGroup.NO_STOP;		} else			return; // nothing happens	}