anchor.diff:          <c:forEach items="${activityTypes}" var="activityType"><option value="${activityType.id}" <c:if test="${selectedActivity.type.id == activityType.id}">selected="selected"</c:if>>${activityType.name}</option></c:forEach>
       </select>
       <select id="add-activity">
  -        <c:forEach items="${activities}" var="activity"><option value="${activity.id}" <c:if test="${selectedActivity.id == activity.id}">selected="selected"</c:if>>${activity.name}</option></c:forEach>
  +        <option>Loading...</option>
       </select>
       <input type="button" id="add-activity-button" value="Add to period"/>
       <a id="newActivityLink" href="<c:url value="/pages/newActivity?returnToPeriodId=${period.id}"/>">Create new activity</a>
  
positive.code:             SC.slideAndShow(rowId)
          }
  
          function showEmptyMessage() {
              if (currentActivityCount() > 0) {
                  SC.slideAndHide('no-activities-message');
  
negative.code:     <title>Set up Period ${period.name} of ${study.name}</title>
      <tags:includeScriptaculous/>
      <script type="text/javascript">
          var activitiesByType = { }
          <c:forEach items="${activityTypes}" var="activityType">
          activitiesByType[${activityType.id}] = []
          </c:forEach>
          <c:forEach items="${activities}" var="activity">
          activitiesByType[${activity.type.id}].push({ name: '${activity.name}', id: ${activity.id} })
          </c:forEach>
          var initiallySelectedActivity = ${empty selectedActivity ? 0 : selectedActivity.id}
  
          function currentActivityCount() {
              return $$('.input-row').length;
          }
  