can someone help explain to me.. what $prop is used for? i read the mirc help file and did not understand it.

here is an example of a code i found..

Code:
alias _get {
  if ($0 == 2) && ($prop == unset) { return $hget($1,$2).unset }
  elseif ($0 == 2) && ($prop == item) { return $hget($1,$2).item }
  elseif ($0 == 2) && ($prop == data) { return $hget($1,$2).data }
  elseif ($0 == 2) && ($prop == $null) {
    if ($hget($1,$2) != $null) { return $iif($ifmatch != ~null,$ifmatch)  }
  }
  elseif ($0 == 1) && ($prop == size) { return $hget($1).size }
  elseif ($0 == 1) && ($prop == $null) { return $hget($1) }
  elseif ($0 == 3) && ($prop == $null) { return $hget($1) } 
  elseif ($0 == 3) && ($prop == item) { return $hget($1,$2).item }
  elseif ($0 == 3) && ($prop == data) { return $hget($1,$2).data }
  else { 
    echo SERIOUS ERROR inform $hget(setup,url) 
    echo PROP:= $prop 
    echo Pars:= $0 
    echo Par1:= $1 
    echo Par2:= $2 
    echo Par3:= $4 
    echo Please type /feedback and submit this error and send it. Thanks
  }
}