Page History

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Navigation patterns that are repeated on web pages MUST be presented in the same relative order each time they appear and MUST NOT change order when navigating through the site.must be consistent in presentation order across website
Skip link must be visible on keyboard focus (or at all times).
Reading order must be logical.
Navigation order of focusable elements must be logical.

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Links and buttons should semantically reflect their functions. Example: Use <a href="..."> for links and <button> for buttons.
Link text should clearly state its purpose.
Link text shouldn't use the word "Link." Example: Say "More information on gummy bears." not "Link to more information on gummy bears."
Indicate that a link will open in a new window. Example: add a new-window icon next to links that open in a new window
Links to files or non-web destinations should tell users what kind of files they are. Example: add "PDF" next to links to PDFs
Enhance focus indicator on focusable elements. Example: instead of the default browser focus, add a colorful, thicker border with a change in background when elements receive focus

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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>.

The heading hierarchy of an iframe SHOULD be designed to fit within the heading hierarchy of the parent document, if possible.
Hidden frames or frames that do not convey content to users SHOULD Hidden frames should also be hidden from assistive technologies using aria-hidden="true".

Important strikethrough text must be supplemented with a text-based method to convey the meaning of the strikethrough.
Important insertion text must be supplemented with a text-based method to convey the meaning of the insertion.

<blockquote> should be used for
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 It shouldn't be used for visual styling alone .The <q> element (for inline quotations) SHOULD NOT be used as the only way to designate quotations(non-quotes).
Code SHOULD should be marked with the <code> element and styled to look different from non-code text. Blocks of code SHOULD be formatted with should use the <pre> element for formatting.
Strikethrough text SHOULD be marked with should use the <del> element.Text designated for insertion SHOULD be marked with
Insertion text should use the <ins> element.
Highlighted text SHOULD be marked with should use the <mark> element.
Critical Important highlighted text SHOULD be supplemented with should have a text-based method to convey the meaning way of the highlighting.

Critical strikethrough text MUST be supplemented with a text-based method to convey the meaning of the strikethrough.
Critical text designated for insertion MUST be supplemented with a text-based method to convey the meaning of the insertionconveying the importance of the text.