How about SHITEMID in the shlwapi DLL? That's supposed to be SH-ITEM-ID.

Nah. That would be INITCOMMONCONTROLSEX. And the related LVM_SORTITEMSEX, DDSCAPSEX, and of course MPR_CREDENTIALSEX_0.

if someone ever figures out the meaning of that phrase it's probably going to summon some cosmic horror that will be the end of us all