Outisde of events it works just the same as $eval()

When used inside the matchtext or window section of an event definition, it tells mIRC to evaluate the contents of that section. For instance:

Code:
; Without $()
on *:text:$me:*:{
  ; This will only match the literal text "$me", since by default mIRC does not evaluate identifiers in the event definition.
}

; With $()
on *:text:$($me):*:{
  ; This will match whatever my current nickname is thanks to the use of $()
}



; Example usage in the window section

on *:text:*:$($mychannels):{
  ; This will match any text in the windows returned by an alias called mychannels
}

alias mychannels {
  ; This returns values so that the text will match in #channel #channel2 and any query window
  return #channel,#channel2,?
}

Spelling mistakes, grammatical errors, and stupid comments are intentional.