Library /sys$common/syshlp/basichelp.hlb Line, Numbers  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Line numbers are optional; you can compile, link and run a BASIC program
  without specifying line numbers.

  BASIC line numbers are positive whole numbers in the range 1  to  32767,
  inclusive.   Numbers  outside  this  range, fractional line numbers, and
  line numbers with embedded spaces or tabs generate errors.  Line numbers
  with  percent  signs  are  flagged  as  a  declining  feature  when  the
  /FLAG=DECLINING qualifier is enabled.  Leading zeroes are ignored.

  In the BASIC environment, if the first line of a  program  has  no  line
  number,  BASIC  assumes  that  the  entire  program is a line-numberless
  program.

  If you have a line-numberless program  that  contains  multiple  program
  units,  the  point at which BASIC breaks each program unit is determined
  by the placement of the statement that terminates the program unit.  Any
  text  that  follows  the  program terminator becomes associated with the
  following program unit.  A program terminator can be any  END  statement
  such as an END PROGRAM statement followed by any valid expression.