optional_depends attr \
                 "--enable-xattr" \
                 "--disable-xattr" \
                 "for Extended Attributes support" &&

optional_depends acl \
                 "--enable-acl" \
                 "--disable-acl" \
                 "for ACL support" &&

optional_depends zlib \
                 "--with-zlib" \
                 "--without-zlib" \
                 "for gzip support through zlib" &&

optional_depends bzip2 \
                 "--with-bz2lib" \
                 "--without-bz2lib" \
                 "for bzip2 support through bz2lib" &&

optional_depends xz-utils \
                 "--with-lzma" \
                 "--without-lzma" \
                 "for xz support through lzma" &&

optional_depends lzo \
                 "--with-lzo2" \
                 "--without-lzo2" \
                 "for lzop support through liblzo2" &&

optional_depends nettle \
                 "--with-nettle" \
                 "--without-nettle" \
                 "for crypto support from Nettle" &&

optional_depends SSL \
                 "--with-openssl" \
                 "--without-openssl" \
                 "for mtree and xar hashes support through SSL" &&

optional_depends libxml2 \
                 "--with-xml2" \
                 "--without-xml2" \
                 "for xar support through libxml2" &&
# make icu usage explicit
if is_depends_enabled $SPELL libxml2;then
  if is_depends_enabled libxml2 icu;then
    depends icu
  fi
fi &&

optional_depends expat \
                 "--with-expat" \
                 "--without-expat" \
                 "for xar support through expat"