protected virtual ProjectElement AddFolderToMsBuild(string folder)
{
ProjectElement newItem;
string itemPath = PackageUtilities.MakeRelativeIfRooted(folder, this.BaseURI);
Debug.Assert(!Path.IsPathRooted(itemPath), "Cannot add item with full path.");
newItem = this.CreateMsBuildFileItem(itemPath, ProjectFileConstants.Folder);
return newItem;
}