Aerospace.org W3C HTML Markup Validation
HTML markup errors and warnings
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Errors:
Bad value “revision” for attribute “rel” on element “link”: The string “revision” is not a registered keyword.
Text not allowed in element “iframe” in this context.
Attribute “about” not allowed on element “article” at this point.
The “frameborder” attribute on the “iframe” element is obsolete. Use CSS instead.
Warnings:
The “navigation” role is unnecessary for element “nav”.
The “main” role is unnecessary for element “main”.
The “article” role is unnecessary for element “article”.
Section lacks heading. Consider using “h2”-“h6” elements to add identifying headings to all sections.
Consider using the “h1” element as a top-level heading only (all “h1” elements are treated as top-level headings by many screen readers and other tools).
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