Add Custom Search Fields to Admin (categories.php)

[lukechanning]

I posted a similar question earlier, but in playing with adding custom search fields to the admin/categories.php, I keep breaking the existing search functionality. Furthermore, I can't get my custom search fields to actually produce results. 

 

With all of that in mind: Is there a comprehensive guide anywhere that details where / what to change to add custom search fields to categories.php? 

 

I've found add one, which is pretty close, and I even tried adding it. But it doesn't seem to "do" anything in OSC 2.3 (doesn't pull any results, though the dropdown works fine). It did help me get closer with my own code, but as stated, still no dice. This is also a similar idea (though customer-facing) and yet I just can't seem to get it there . . .

 

So! Obviously not asking for a "Do it for me!" But since I can't find a thread detailing this, I thought others might also appreciate a detailed look at adding search fields to admin/categories.php for non-vanilla items. If it's the best reference, let's roll with the products manufacturer idea, like in that add-on.