Umww.com W3C HTML Markup Validation
HTML markup errors and warnings
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Errors:
Bad value “https://api.w.org/” for attribute “rel” on element “link”: The string “https://api.w.org/” is not a registered keyword.
An “img” element must have an “alt” attribute, except under certain conditions. For details, consult guidance on providing text alternatives for images.
Attribute “webkitallowfullscreen” not allowed on element “iframe” at this point.
Attribute “mozallowfullscreen” not allowed on element “iframe” at this point.
The “frameborder” attribute on the “iframe” element is obsolete. Use CSS instead.
Bad value “” for attribute “src” on element “img”: Must be non-empty.
Duplicate ID “link-to-tweet”.
Duplicate ID “fave-tweet”.
Duplicate ID “reply-to-tweet”.
Warnings:
Consider avoiding viewport values that prevent users from resizing documents.
The first occurrence of ID “link-to-tweet” was here.
The first occurrence of ID “fave-tweet” was here.
The first occurrence of ID “reply-to-tweet” was here.
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