$isdde(text) Returns $true if the specified dde name is in use, $false otherwise.
* N = The DDE name you want to check for.
It will return $true if the currently mIRC using DDE name is the one that you specified, otherwise will be $false.
NOTE: The default mIRC dde name is "mIRC", if you would never change that from the options then is gonna be that for ever.
Added: mIRC v5.41
Added on: 24 Jul 1998
Note: Unless otherwise stated, this was the date of original functionality.
Further enhancements may have been made in later versions.