Bookdown.org W3C HTML Markup Validation
HTML markup errors and warnings
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Errors:
A document must not include both a “meta” element with an “http-equiv” attribute whose value is “content-type”, and a “meta” element with a “charset” attribute.
Element “a” not allowed as child of element “ul” in this context. (Suppressing further errors from this subtree.)
Duplicate ID “content”.
Bad value “120px” for attribute “width” on element “iframe”: Expected a digit but saw “p” instead.
Bad value “20px” for attribute “height” on element “iframe”: Expected a digit but saw “p” instead.
The “frameborder” attribute on the “iframe” element is obsolete. Use CSS instead.
The “scrolling” attribute on the “iframe” element is obsolete. Use CSS instead.
The element “iframe” must not appear as a descendant of the “a” element.
Start tag “a” seen but an element of the same type was already open.
End tag “a” violates nesting rules.
Cannot recover after last error. Any further errors will be ignored.
Warnings:
The first occurrence of ID “content” was here.
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