<% Story.topicchooser %>
macro renders a list of existing topics as dropdown

Sourcecode in Story/macros.js:
1:   function topicchooser_macro(param) {
2:      var size = path.Site.topics.size();
3:      var options = new Array();
4:      for (var i=0;i<size;i++) {
5:         var topic = path.Site.topics.get(i);
6:         if (topic.size()) {
7:            options[i] = {value: topic.groupname, display: topic.groupname};
8:            if (req.data.addToTopic)
9:               var selected = req.data.addToTopic;
10:           else if (this.topic == topic.groupname)
11:              var selected = topic.groupname;
12:        }
13:     }
14:     Html.dropDown({name: "addToTopic"}, options, selected, param.firstOption);
15:     return;
16:  }