Youscience.com W3C HTML Markup Validation
HTML markup errors and warnings
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Errors:
The “charset” attribute on the “link” element is obsolete. Use an HTTP Content-Type header on the linked resource instead.
Bad value “https://api.w.org/” for attribute “rel” on element “link”: The string “https://api.w.org/” is not a registered keyword.
Duplicate ID “main-nav”.
Saw “<!--” within a comment. Probable cause: Nested comment (not allowed).
An “img” element must have an “alt” attribute, except under certain conditions. For details, consult guidance on providing text alternatives for images.
The “aria-controls” attribute must point to an element in the same document.
Warnings:
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).
Section lacks heading. Consider using “h2”-“h6” elements to add identifying headings to all sections.
The first occurrence of ID “main-nav” was here.
The document is not mappable to XML 1.0 due to two consecutive hyphens in a comment.
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