(PHP 5 >= 5.3.0, PHP 7, PHP 8, PECL phar >= 2.0.0)
Phar::isWritable — Returns true if the phar archive can be modified
   This method returns true if phar.readonly is 0,
   and the actual phar archive on disk is not read-only.
  
No parameters.
   Returns true if the phar archive can be modified