ircII help: bind command_completion

Usage: BIND <key> COMMAND_COMPLETION
  The COMMAND_COMPLETION function will cause IRCII to attempt to
  complete the command you have typed in the input line.  If a
  match is found, it is expanded to its full length in the input
  line.  If multiple matches are found, the complete list of
  matching commands is displayed.  If no match is found, the
  input line is left unchanged.