Focus order is also similar to reading order. However focus order is more concentrated on interactive elements such as links and forms.
For instance a marketing subscription form have Name, email address , phone text boxes on left-hand side and news articles, blogs and marketing adds check boxes on right-hand side with a submit button. When the user navigate it with a keyboard, it may start at Name, move to news checkboxe, then to phone number and then to blog check box , then to email address, then to marketing adds checkbox and finally to submit button. The order is absolutely illogical.
The other problem with focus order is often submitting a form, opening the modals, navigating within tabs, treeview items etc. How logical is the pushed focus? The focus requirements and the focus management is discussed in the next chapter.