optional_depends icu \
                 "--with-icu" \
                 "--without-icu" \
                 "Unicode support" &&

optional_depends zlib \
                 "--with-zlib=${INSTALL_ROOT}/lib" \
                 "--without-zlib" \
                 "to build with zlib support" &&

optional_depends xz-utils \
                 "--with-lzma=${INSTALL_ROOT}/usr/lib" \
                 "--without-lzma" \
                 "to build with LZMA support" &&

optional_depends PYTHON \
                 "--with-python" \
                 "--without-python" \
                 "to build python bindings"

.