With regards to THIS_SCRIPT
 

So I've been checking a few threads here and there and a question comes to mind about THIS_SCRIPT. Can you define any php page? For example define('THIS_SCRIPT', 'hotdogs'); would highlight a tab called hotdogs that goes to a page called /hotdogs.php (assuming you define it).

Basically I want to create some custom pages and tabs for them but not hassle with plugins for the tabs to stay highlighted.

Right - I think. If you make a custom script and in it define THIS_SCRIPT to be 'hotdogs', and you create a tab and put hotdogs in the This Script field, then whenever you go to your custom script that tab should be selected.

How is this done?

I see that you've found the article on creating your own page. You can see in that code there's already a line near the top that defines THIS_SCRIPT. So lets say you call your new file about.php, and at the top you change the THIS_SCRIPT line to be

Then you can go to the navigation manager and create an About tab, you could set your "target url" to about.php and in "Tab Script(s)" at the bottom, enter "about" (no quotes) so that your About tab will be selected whenever THIS_SCRIPT is defined as 'about'.