anchor.diff:      call h5gcreate_f(file_id, 'observables', g_id, h5_error)
       call h5gclose_f(g_id, h5_error)
   
  -  end subroutine h5md_open_file
  +  end subroutine h5md_create_file
   
     !> Adds a trajectory group in a h5md file
     !! @param group_name name of a subgroup of 'trajectory'.
  
positive.code:   
  contains
  
    !> Opens a h5md file
    !!
    !! Creates the '/h5md' group and gives it the attributes 'creator' and 
    !! 'version'. currently, only supports creating a new file.
  
negative.code:   !! @param file_id the returned hdf5 location of the file.
    !! @param filename name of the file.
    !! @prog_name name that appears in the 'creator' global attribute.
    subroutine h5md_create_file(file_id, filename, prog_name)
      integer(HID_T), intent(out) :: file_id
      character(len=*), intent(in) :: filename, prog_name
  
  