[citation needed]
I see a grand total of 3 posts that talk about the spelling:
One in the proposal thread by David Abrahams suggesting “rotateFirstFrom”.
One in the review thread by Dmitri Gribenko suggesting “'rotate(shiftingToStart:)”.
One immediately after that by Nate Cook agreeing that the base name should be “rotate”.
I maintain my claim that “startingAt” is a more clear and concise label than “shiftingToStart”. Compare:
rotate(startingAt: i)
rotate(shiftingToStart: i)