code: public Range getRange() {
  		String value = first(RANGE);
  		return (value == null) ? null : Range.get(value);
  	}
docs: <p>
  Gets the RANGE parameter value.
  </p>
  <p>
  This parameter is used by the {@link RecurrenceId} property. It defines
  the effective range of recurrence instances that the property references.
  </p>
  @return the range or null if not set
  @see <a href="http://tools.ietf.org/html/rfc5545#page-23">RFC 5545
  p.23-4</a>