docs: def attach(names, parent, dry_run, verbose):
      """Attach collection(s) to a parent."""
      parent = Collection.query.filter_by(name=parent).one()
      collections = Collection.query.filter(Collection.name.in_(names)).all()
      for collection in collections:
          collection.move_inside(parent.id)
          if verbose:
              click.secho(
                  'Collection "{0}" is being attached to "{1}".'.format(
                      collection.name, parent
                  ), fg='green')