I have another couple of suggestions.

The first suggestion is to add

     export -f :

just before the fi so that it is available to scripts called from the main script.

The second is to add

  local IFS=" " # Insulate : from changes to IFS

before the printf.

because if I didn't then each word of the comment would appear on a separate line like this:

  ::
  a
  b
  c

instead of this:

  :: a b c

the reason for this is that I had defined

  IFS="/n/t"

as suggested by the Unofficial Strict Mode.