multiple applications

[eluser]Unknown[/eluser]
I tried to follow:
http://codeigniter.com/wiki/Multiple_Applications/

And, I attempted to setup the fully general case at the bottom:
/CodeIgniter_x.x.x/
/system/
/application/
/frontend/
/backend/
/webroot
index.php
.htaccess

But, there were some details left out of that page. After some trial and error, I have it working, but either I'm misunderstanding what "baseurl" is used for, or there are problems :-)

The part of index.php that I changed:
//$application_folder = "application";
$application_folder = MY_BASE_FILE_SYSTEM_DIR . '/application/a';
$uriArr = explode("/", $_SERVER['REQUEST_URI']);
if(count($uriArr) > 1){
switch($uriArr[1])
{
case 'b':
$application_folder = MY_BASE_FILE_SYSTEM_DIR . '/application/b';
break;

case 'c':
$application_folder = MY_BASE_FILE_SYSTEM_DIR . '/application/c';
break;
}
}

I figured this would support all four of these cases:
http://host/a
http://host/b
http://host/c
http://host/ (maps to a)

In .htaccess I have:
writeEngine on
RewriteCond $1 !^(index\.php|images|robots\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]
(from the user guide)

In each application, I had to change config.php (this is under "a"):
$config['base_url'] = "http://" . MY_HOST_NAME . "/a/";
$config['index_page'] = "";

But, now for the madness. I assumed that:
http://host/a/class/method
Would hit class's method (since http://host/a is the base url). But, I kept getting 404 errors. For some random reason, I created a controller called "a", and it loaded! This made no sense to me as it seemed like codeigniter was treating "a" as the class?? Based on this, I modified routes.php:
$route['a/(.*)'] = "$1";

And, this works! So, for some reason, in application "a", even though I defined the baseurl as http://host/a, I have to manually strip off the "a" from the route to get things to line up?

If this really is correct, I can update the wiki. But, it seems really weird to me.

will