WebAIM: Creating Accessible Frames & iFrames
This Guide uses iframes (inline frames). WebAIM indicates "There are no distinct accessibility issues with inline frames. The content of the inline frame is read at the point it is encountered (based on markup order) as if it were content within the parent page."
We will need to test to make sure. All Guide pages here using iframes also provide a direct link to the document, PDF, or spreadsheet within CyBox, all of which have been checked as accessible in themselves.