SRV_VRFY_CLT
bitset(SRV_VRFY_CLT, features));
bitset(SRV_VRFY_CLT, features))
{ 'R', SRV_VRFY_CLT }, /* same as V; not documented */
{ 'V', SRV_VRFY_CLT },
: SRV_VRFY_CLT)