You can place an empty "expansion" in that line to get the behavior you want without an additional cat-like function foo`'bar I only know of this feature

You can place an empty "expansion" in that line to get the behavior you want without an additional cat-like function foo`'bar I only know of this feature because recently read the manual page for m4, and it's mentioned rather early in there, but might have been not as well emphasized in past iterations of the manual.