how do I delete a file from time machine backups?

Thanks for your reply. So I guess the file remains in Time Machine backups until the space allocated for those backups gets filled up and new backups overwrite them? Either that or you have to just reformat the external drive (or sector on that drive where the backups are store) and start your backups all over? Doesn't seem like they give you good options if you have a file you want to delete everywhere.

I really appreciate your feedback. In my ignorance, I would have thought the purpose of time machine would be to faithfully backup your desired contents to allow later access at various points in time. Since it allows you to exclude items from backup, it would seem they would also allow you to delete those items from the backup if later determined you did not want to retain them there. Anyway, I get your point, and thanks again.