How to use libunistring (GNU Gnulib)

There are three ways to use GNU libunistring:

You can declare GNU libunistring as a prerequisite of your package and then, at build time, link with the installed libunistring. To achieve this, use the Gnulib module libunistring.
You can include the source code of specific libunistring modules in your package, through the usual Gnulib mechanism. Then, there is no prerequisite.
A combination of both: You can declare GNU libunistring as an optional prerequisite of your package and include the source code of specific libunistring modules in your package. At configure time, when the user has specified the configure option --with-included-libunistring, the included modules will be used and the package will not link against an installed libunistring. Otherwise, the package will link against an installed libunistring if found, and only those modules will be built that are not contained or that are too old in the found libunistring. To achieve this, request from Gnulib the specific modules and the Gnulib module libunistring-optional.