This will keep a window open where your highlighted messages will be kept. It's still work in progress because, even though the @highlights window content is logged to a file, I haven't found an easy (emphasis on "easy") way to load the logfile into the highlights window on startup. At least not when there's a date in the filename.

;Highlights Window by Tritonio

on *:TEXT:*:#: {
  if ($highlight($1-)) {
    echo 9 @highlights $chan $+ : $1-
  }
}

alias resethighlights {
  close -a@ @highlights
  window @highlights
  log on @highlights
  loadbuf 20 @highlights @highlights.log
}

on *:START:{
  resethighlights
}