Guide, Programming in Makefiles: Why trailing '' in example 3?

["J. Lewis Muir" <jlmuir%imca-cat.org@localhost>]

Hello, all.

In section 12.3.2, Echoing a string exactly as-is, of the pkgsrc guide
at:

  https://www.netbsd.org/docs/pkgsrc/makefile.html#echo-literal

example 3 is:

  printf '%s\n' ${STRING:Q}''

What is the purpose of the two trailing single quote characters?

Thanks!

Lewis