PropertyMgr.evalCache ()
checks if the cache is still up to date and (re-)creates the cache if necessary

Sourcecode in PropertyMgr/objectFunctions.js:
1:   function evalCache() {
2:      if (this.cache.content == null) {
3:         var fieldName = this.getDataField();
4:         // cache is either outdated or not existing, so (re-)create it
5:         if (this._parent[fieldName] && this._parent[fieldName].trim() != "") {
6:            this.cache.rawcontent = this._parent[fieldName];
7:            this.cache.content = Xml.readFromString(this.cache.rawcontent);
8:         } else {
9:            this.cache.rawcontent = "";
10:           this.cache.content = new HopObject();
11:        }
12:     }
13:     return;
14:  }