/** Produces an indented XML representation of this object. */
 public StringBuffer toXML() {
   StringBuffer sb = new StringBuffer(500);
   sb.append("<ogc:").append(getOperatorName()).append(">");
   sb.append(expr1.toXML());
   sb.append(expr2.toXML());
   sb.append("</ogc:").append(getOperatorName()).append(">");
   return sb;
 }