defined. Many of them are only useful in very specific cases, typical packages
will therefore only use a few of them.
+* +FOO_SUBDIR+ may contain the name of a subdirectory inside the
+ package that contains the main meson.build file. This is useful,
+ if for example, the main meson.build file is not at the root of
+ the tree extracted by the tarball. If +HOST_FOO_SUBDIR+ is not
+ specified, it defaults to +FOO_SUBDIR+.
+
* +FOO_CONF_ENV+, to specify additional environment variables to pass to
+meson+ for the configuration step. By default, empty.