To add custom content to the "Write" admin pages (where you write posts, pages or links), WordPress 2.5 introduces a new function set: add_meta_box() Simple plugin example : The catch here is to hook the function that add our "meta box" (here: add_some_box()) late enough so that the function it needs, add_meta_box(), has been defined. Hooking on 'admin_menu' is fine.…