Page History

...

Tabular data should use HTML table semantics.
Data tables should have an associated caption or name that describes table accurately, and be unique.
Provide a data table summary to make it easier for screen reader users
Don't use tables for non-data page layout

iFrames

must have a descriptive title Example: <iframe title="Star Wars: The Last Jedi trailer"> and be unique in relation to other iFrames on the page
for iframes bringing in other web pages, the external page must have a <title>
iframes that convey content to users MUST have a non-empty title attribute.
The iframe title MUST be accurate and descriptive.
Frames MUST have a unique title (in the context of the page).
The source page of an iframe MUST have a valid, meaningful <title>.

...

Critical emphasis in the text SHOULD be conveyed through visual styling.
Critical emphasis in the text SHOULD be conveyed in a text-based format.
The <blockquote> element SHOULD be used to designate long (block level) quotations.
The <blockquote> element SHOULD NOT be used for visual styling alone.
The <q> element (for inline quotations) SHOULD NOT be used as the only way to designate quotations.
Code SHOULD be marked with the <code> element and styled to look different from non-code text.
Blocks of code SHOULD be formatted with the <pre> element.
Strikethrough text SHOULD be marked with the <del> element.
Text designated for insertion SHOULD be marked with the <ins> element.
Highlighted text SHOULD be marked with the <mark> element.
Critical highlighted text SHOULD be supplemented with a text-based method to convey the meaning of the highlighting.

...