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

  A channel expression is a numeric expression that  specifies  a  channel
  number  associated  with  a  file.  A file must be open on the specified
  channel or BASIC  signals  an  error.   A  channel  expression  must  be
  preceded by a pound sign (#).