Today, while writing a QueryRange, I had to pass a blank InventDimid. Initially, to make life easier ;-). I just put "BLANK".
Then, just did a bit of search and found that InventDim has a static method inventDimIdBlank which was exactly what I required. It returns "AllBlank". Many of you guys might be knowing this one, but just for the ignorant out there (including me) :-) this is a handy tip