I feel like the documentation would be more clear if instead of "element" it said which specific kind of element it means (packets and bytes depending on the kind of the socket). Also, please add dots at the end of sentences.

packets and bytes depending on the kind of the socket

The current methods only describe the capacities of the payload buffers, which are all bytes. Would you like me to add capacity methods for meta buffers for the socket types that support it (udp, icmp etc) too?

The current methods only describe the capacities of the payload buffers, which are all bytes. Would you like me to add capacity methods for meta buffers for the socket types that support it (udp, icmp etc) too?

Oh, good point. For those sockets, we should not have a single capacity method but two different ones. What about payload_capacity and packet_capacity?