I know I can customize my 404 page. This guy suggests "At wordpress, customize your “404 – Not Found” error page to have a search box, categories (tags in Blogger), Archive to have visitor to browse through your blog. This is necessary because Blogger Permalinks to post are different from wordpress permalinks & visitors from search engines will come to “404 – Not Found” page."
I don't know how to add the code for a serach box and categories to my 404 page, which I know I can edit in the theme editor. Can anyone point me to documentation that explains how to do so?