(d) Documents shall be organized so they are readable without requiring an associated style sheet.
The obvious meaning to this one is that if you use style to organize your web page it must be presented readably and in the correct order even if CSS styles are turned off. All you have to do to comply with this requirement is assemble your page in a logical order.
The less obvious consideration for this requirement is how you pages are organized. Screen readers provide their users with page organization cues through the header tags. Because of this you must keep the header tags organized so they conform to standard outline format. Header tags should begin on a page with H1 and follow each other consecutively as they are added, just like in MLA outline format. For example, H1-H2-H2-etc is okay. H1-H3 would violate the outline rules, as would H2-H2-H1.
An added benefit to this rule is that you should be organizing your pages like this anyway. It is, simply put, a good practice.
The Firefox Web Developer's Toolbar (WDTB) provides a good way to check your page's organization: Publish the page, view it in Firefox and use the WDTB's Information Menu. About three quarters down the menu select View Document Outline
and it will tell you if any of your header tags are out of order, as in the following two examples:
 A test result from View Document Outlineshows that the page lacks an H2 header element. |
 A test result that indicates a correctly organized page. |
