Look at the 'blocks' method in the PHP outputrenderers.php file and see how it works and calls other methods to understand what I've written. Greater detail = pages and pages of explanation depending on your PHP skill level, Moodle knowledge and understanding of Object Orientated programming = thus I don't know this at this point in time. And sorry, I don't have the time to write a highly granular explanation.
With 'defaultregion' try 'content'. Its more of a hunch as that block region is not specifically listed in the config.php file.
With 'defaultregion' try 'content'. Its more of a hunch as that block region is not specifically listed in the config.php file.