gistfile1.php

<?php
class regions {
    static function initialize()
    {
        // We need to process the_content as early as possible, to be sure that DOM tree identical to edited one
        // Also, function accept 2 arguments, so when needed we can supply exact regions to apply
        if ( !is_admin() ) { // We don't want to run this on the backend
            if (true) { // until apply_filter use current()/next()
                add_filter('the_content', array(self::instance(), 'content_split_join'), -99991, 2);
            } else {
                // Use split/join to proceed every piece independently
                add_filter('the_content', array(self::instance(), 'content_split'), -99991, 2);
                add_filter('the_content', array(self::instance(), 'content_join'), +99991);
            }
        }
    }
}