* https://github.com/inaka/sumo_rest/blob/0.3.3/src/sr_state.erl#L42

  * Function spec may be further detailed, but that would require type
    spec and new internal type (for mandatory key);

  * Having a field and exported function for id is enough.

* https://github.com/inaka/sumo_rest/blob/0.3.3/src/sr_single_entity_handler.erl#L43

  * It already comments on the :id element of cowboy route clearly.

* https://github.com/inaka/sumo_rest/blob/0.3.3/src/sr_request.erl#L18

  * Added internal type for documentation purpose.

* https://github.com/inaka/sumo_db/blob/0.7.1/src/sumo_internal.erl#L88

  * See inaka/sumo_db#294

* https://github.com/inaka/sumo_rest/blob/0.3.3/test/sr_test/sr_single_session_handler.erl#L60
  and
  https://github.com/inaka/sumo_rest/blob/0.3.3/test/sr_test/sr_single_element_handler.erl#L66

  * They already mention `:id` clearly;

  * The only source of confusion may be whether the name of the
    parameter in the Swagger schema
    e.g. [this](https://github.com/inaka/sumo_rest/blob/0.3.3/test/sr_test/sr_single_element_handler.erl#L33)
    needed to be called `id` e.g. in case cowboy_swagger enforces it.

* https://github.com/inaka/sumo_rest/blob/0.3.3/README.md

  * It already mentions `:id` clearly.