debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
nls - Add Native Language Support (using gettext - GNU locale utilities)
ssl - Add support for SSL/TLS connections (Secure Socket Layer / Transport Layer Security)
static-libs - Build static versions of dynamic libraries as well