public java.io.Serializable fromDOM(Document document) {
		Map e2t = elementsToText(document.getDocumentElement());
		String expression = (String) e2t.get(EXPRESSION_NAME);
		if (expression == null)
			if (e2t.containsKey(EXPRESSION_NAME))
				throw new ParseException("Regular expression structure has no "
						+ EXPRESSION_NAME + " tag!");
			else
				expression = "";
		return new RegularExpression(expression);
	}