code: public void add(final Field _field)
      {
          this.fields.put(_field.getId(), _field);
          this.fieldName2Field.put(_field.getName(), _field);
          if (_field.getReference() != null && _field.getReference().length() > 0) {
              final String ref = _field.getReference();
              int index;
              int end = 0;
              while ((index = ref.indexOf("$<", end)) > 0) {
                  index += 2;
                  end = ref.indexOf(">", index);
                  addFieldExpr(ref.substring(index, end));
              }
          }
          _field.setCollectionUUID(getUUID());
      }
docs: Method to add a Field to this Collection.
  
  @param _field Field to add to this collection