If a file is brought in from another open-source project, a DocBlock MUST be added that clearly names the origin in the @copyright tag.

Example:

/**
* @copyright Copyright (c) 2009-2014 FooBar
*/


If a component of the FooBar project is refactored, the unchanged code establishes a baseline. If this component does not use SemVer versioning, the unchanged baseline MUST be denoted as @version 0.0.0 for reference purposes:

/**
* @copyright Copyright (c) 2009-2014 FooBar
* @version 0.0.0
*/


Once the file is changed, copyright (or, actually, copyleft) is extended to the StoreCore framework:

/**
* @copyright Copyright (c) 2016 StoreCore
* @copyright Portions copyright (c) 2009-2015 FooBar
* @version 0.1.0
*/


Please note that documenting changes and proper attribution is REQUIRED by the GNU General Public License (GPL):

For the developers’ and authors’ protection, the GPL clearly explains that there is no warranty for this free software. For both users’ and authors’ sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions.)