optional_depends tiff \
                 --with{,out}-libtiff \
                 "for TIFF support" &&

optional_depends libpng \
                 --with{,out}-libpng \
                 "for PNG support" &&

optional_depends libxml2 \
                 --with{,out}-libxml \
                 "for XML meta-data?" &&

optional_depends zlib \
                 --with{,out}-zlib \
                 "for Zlib compression?" &&

optional_depends SSL \
                 --with{,out}-openssl \
                 "for DICOM security extensions" &&

optional_depends libsndfile \
                 --with{,out}-libsndfile \
                 "for Sound support" &&

optional_depends tcp_wrappers \
                 --with{,out}-libwrap \
                 "TCP wrapper access control"

.