http://php.net/manual/en/function.array-push.php#refsect1-function.array-push-description > Note: If you use array_push() to add one element to the array it's better to use $array[] = because in that way there is no overhead of calling a function.
Because even if it doesn't make a difference in practice, it is technically more correct to call static methods statically. It also better advertise that those methods can be used from any context.
This is to prevent color changing when copy/pasting xls files written by PhpSpreadsheet to another file. Closes #218