BitSet within(Token instruction, BitSet bs) throws ScriptException {
		Object withinSpec = instruction.value;
		if (withinSpec instanceof Float)
			return viewer.getAtomsWithin(((Float) withinSpec).floatValue(), bs);
		if (withinSpec instanceof String) {
			String withinStr = (String) withinSpec;
			if (withinStr.equals("element") || withinStr.equals("site") || withinStr.equals("group")
					|| withinStr.equals("chain") || withinStr.equals("molecule") || withinStr.equals("model"))
				return viewer.getAtomsWithin(withinStr, bs);
			return viewer.getAtomsWithin("sequence", withinStr, bs);
		}
		evalError(GT._("Unrecognized {0} parameter", "WITHIN") + ":" + withinSpec);
		return null; // can't get here
	}