For data tables that have two or more logical levels of row or column headers, use markup to associate data cells and header cells.

Point 6.1:

Organize documents so they may be read without style sheets. For example, when an HTML document is rendered without associated style sheets, it must still be possible to read the document.

Point 6.2:

Ensure that equivalents for dynamic content are updated when the dynamic content changes.

Point 6.3:

Ensure that pages are usable when scripts, applets or other programmatic objects are turned off or not supported. If this is not possible, provide equivalent information on an alternative page.