You don't want the footer or navigation in the output. Ideally you want the main content of the page, if it exists. How do you assign header level if they're on

You don't want the footer or navigation in the output. Ideally you want the main content of the page, if it exists. How do you assign header level if they're only differentiated by CSS left-margin in a variety of units? How do you interpret documents that render properly but are hardly correct HTML?