code: function pickUnits(dest, settings) {
          var units = settings.units;
          if (!isArray(units)) {
              error("Invalid units array in pick settings");
          }
          if (!(settings.namespace instanceof Gumup)) {
              error("Invalid namespace in pick settings");
          }
          var picked = {},
              srcDecls = settings.namespace._declarations;
          for (var i = 0, len = units.length; i < len; i++) {
              var reqName = units[i];
              if (!checkRequireName(reqName)) {
                  error("Invalid unit name '" + reqName + "' in pick settings");
              }
              forEach(srcDecls, reqName, function(depName) {
                  pickUnit(srcDecls, dest._declarations, depName, picked, {});
              });
          }
      }
docs: Iterate over `settings.unit`, executing a `pickUnit` function for each item.