I see the ishow function description in the manual is duplicated as just the "show" function.
The "show" function is the next description just after the rename function description and before the flipflag.
I would think the show function description should be removed from the manual, because there is not a show function in the tensor package.
Sorry, my preceding comment about SIMPLIMSUBST was misplaced. Sorry for the bother, I've moved it to the appropriate place.
No worries.
Fixed. Looks like someone moved an obsolete function definition from another texi file 10 (!!!) years ago and you're the first to notice! Also updated makebox.
Fixed by commit b83a40, thanks Viktor.