title: How can I add custom fields to WordPress's built-in taxonomy meta boxes?
body: <p>Specifically, I want to add a couple fields to the Categories meta box ('categorydiv'). I was hoping there would be a filter, but I couldn't find one. I know I can create a custom meta box, but it will be easiest for my client if they see these fields tied to choosing a category. The visual break of a new meta box is undesirable, and it would be unacceptable to have it appear anywhere but immediately below Categories (e.g., under Tags).</p>