optional_depends zlib \
                 "--with-zlib=$INSTALL_ROOT/lib --with-zinc=$INSTALL_ROOT/include" \
                 "--without-z" \
                 "for data compression support" &&

optional_depends pcre \
                 "--with-pcre" \
                 "--without-pcre" \
                 "for regular expressions support" &&

optional_depends libpng \
                 "--with-png" \
                 "--without-png" \
                 "for PNG image manipulation support" &&

optional_depends readline \
                 "--with-readline" \
                 "--without-readline" \
                 "to use GNU readline instead of slang for slsh"
