docs: function assertStrictOptions(funcname, opts, expected) {
      assert.object(opts, 'opts');
  
      for (var k in opts) {
          if (!opts.hasOwnProperty(k)) {
              continue;
          }
  
          var e = expected[k];
          if (!e) {
              throw (new Error(funcname + ': unexpected option: ' + k));
          }
  
          assert[e](opts[k], 'opts.' + k);
      }
  }