Template hirarchy for 404

[mark-k]

load 404-{post-type}.php when url structure matches post permalink structure but there is no post at that address.

load 404-{taxonomy}.php when url structure matches taxonomy permalink structure but doesn't match any specific taxonomy tag URL.

And so on....

The idea is to have different 404 pages based on the context to which the URL refers. For example if a site has a blog and a shop it might be better to show a blog specific 404 page when the URL might be interpreted as a post and a shop specific 404 page when the URL might be interpreted as a product.