HTML Checking for Large Sites

A button element, or an element with the role=button attribute, is not allowed to be nested inside an <a> element.

A button element cannot contain a descendant element with the attribute tabindex.

The href attribute of an <a> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.

The target attribute on <a> elements can’t be blank.

This attribute defines the browsing context for links, that is, where should the linked documents be opened. This was used extensively on the now deprecated <frame> element, so you could give the name of the frame to open the document in, but is now more used to force links to open in a separate tab or window using target="_blank". Another option is using a name, so the new browsing context can be referred to on subsequent clicks on links with the same target.

For example, this will force the links to open on a new tab:

<a href="https://example.com" target="_blank">will open a blank tab</a>

The href attribute on an a tag expects a valid URL, but only http:// was found.

<a> tags can be used to link to an email address using the mailto protocol in the href attribute. Ensure that there is no space in the email address.

<a href="mailto: liza@example.com">This is wrong as it contains an space</a>

<a href="mailto:liza@example.com">This is OK</a>

Space characters are not allowed in href attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:

<a href="https://example.com#some term">invalid</a>
<a href="https://example.com#some%20term">valid</a>

The href attribute on an <a> tag contains an space, which is not allowed. Consider replacing space characters with “%20”.

The value used in the target property of an <a> element has been identified as a keyword because it starts with an underscore _, but it’s not a valid keyword.

Values starting with an underscore for the target property are used for reserved keywords like _blank, _self, _parent or _top.

The value provided on the type attribute of an a element is not a valid MIME type.

The type attribute expects a MIME type that hints at the linked URL’s format.