code: function getDoc (docName, qs0, callback0) {
        const { opts, callback } = getCallback(qs0, callback0)
  
        if (!docName) {
          if (callback) { callback(new Error('Invalid doc id'), null) }
        } else {
          return relax({ db: dbName, doc: docName, qs: opts }, callback)
        }
      }
docs: http://docs.couchdb.org/en/latest/api/document/common.html#get--db-docid