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 python3 \
                 "--with-python=yes" \
                 "--without-python" \
                 "to build python bindings" &&

if is_depends_enabled $SPELL python3; then
  depends doxygen
  else
  optional_depends doxygen \
                   "--with-docs" \
                   "--without-docs" \
                   "for documentation" &&
  if is_depends_enabled "${SPELL}" "doxygen"; then
    depends libxslt &&
    depends docbook-xsl
  fi
fi