code: public boolean add(BtrpElement el) {
          switch (el.type()) {
              case VM:
                  if (!this.vms.add((VM) el.getElement())) {
                      return false;
                  }
                  break;
              case NODE:
                  if (!this.nodes.add((Node) el.getElement())) {
                      return false;
                  }
                  break;
              default:
                  return false;
          }
          return true;
  
      }
docs: Add a VM or a node to the script.
  
  @param el the element to add
  @return {@code true} if the was was added