#BuffDesc is the second line of the tooltip of the buff selected by #BuffIndex:
usually what the buff does, such as the stat bonus. It is processed like #BuffName:
client language, arguments filled in, markup dropped, spaces as _.
It also reads N/A for a buff without a description. Reads N/A when no buff is selected: the buff bar is closed or empty, the client’s buff bar layout is not
supported, or the selected buff has left the bar since the last ScanBuffs or
set #BuffIndex.