I want to add a meta box to the menu page. More specifically I want to basically clone the pages or category meta box and have it load the items into the list from a meta key, instead of pages or categories.
My theme is one page, so users create content for the front page with posts. When users make posts on my theme it has the option to add an ID(it adds it into the code) so a menu item can be added to the top menu and when it is clicked it will scroll to that item with that id. The way it currently works is the user enters the ID and then on the front-pages code I added some code to pull all items from the metakey and populate the menu.
With this I have had many problems so I would rather have a meta box on the menu page with the sections(posts) already populated so the user can choose what sections(posts) they want to add to the menu. Hence I think I could just use the category or pages meta box code and modify it to my needs, so it leads me to my question: Where can I find the code for the menu page meta boxes?