void history(int pt) throws ScriptException {
		if (statementLength == 1) {
			// show it
			showString(viewer.getSetHistory(Integer.MAX_VALUE));
			return;
		}
		if (pt == 2) {
			// set history n; n' = -2 - n; if n=0, then set history OFF
			checkLength3();
			int n = intParameter(2);
			if (n < 0)
				invalidArgument();
			viewer.getSetHistory(n == 0 ? 0 : -2 - n);
			return;
		}
		switch (statement[1].tok) {
		// pt = 1 history ON/OFF/CLEAR
		case Token.on:
		case Token.clear:
			viewer.getSetHistory(Integer.MIN_VALUE);
			return;
		case Token.off:
			viewer.getSetHistory(0);
			break;
		default:
			keywordExpected();
		}
	}