code: function pickUnit(srcDecls, destDecls, name, picked, stack) {
          var decl = srcDecls[name];
          if (!picked[name]) {
              if (stack[name]) {
                  error("Recursive dependency '" + name + "'");
              }
              stack[name] = true;
              for (var i = 0, len = decl._dependencies.length; i < len; i++) {
                  var reqName = decl._dependencies[i];
                  forEach(srcDecls, reqName, function(depName) {
                      if (depName !== name) {
                          pickUnit(srcDecls, destDecls, depName, picked, stack);
                      }
                  });
              }
              destDecls[name] = decl;
              picked[name] = true;
          }
      }
docs: Copy unit declaration and its dependencies.