code: function forEachFilename( files, callback ) {
      files.forEach( function ( file ) {
        file.src.forEach( function ( src ) {
          if ( ! grunt.file.exists( src ) ) {
            grunt.verbose.writeln( 'source file "' + src + '" not found' );
            return false;
          }
  
          if ( grunt.file.isDir( src ) ) {
            grunt.verbose.writeln( 'source file "' + src + '" seems to be a directory' );
            return false;
          }
  
          var filename = path.relative( file.orig.cwd, src );
  
          callback( src, filename, file.dest, file.orig.cwd );
        });
      });
    }
docs: keeping it DRY