HTML Guide

An </a> end tag has been found to violate nesting rules. <a> tags can’t include other <a> tags inside. Most probable cause is an unclosed <a> tag, like in this example:

<a href="one.html">Page 1
<a href="two.html">Page 2</a>

A <button> tag can’t include other <button> tags inside. Most probable cause is an unclosed <button> tag, like in this example:

<button>Submit
<button>Cancel</button>

The <iframe> HTML element represents a nested browsing context, embedding another HTML page into the current one.

As the iframe is a container that holds an embedded HTML page, it cannot be nested inside an a tag.

An <input> tag can’t be used inside an <a> tag.

A <label> tag can’t be used inside an <a> tag. Consider using other tags like <span>.

A <textarea> tag can’t be used inside an <a> tag.

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

An <a> 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.

Space characters are not permitted in the value of the href attribute; they must be properly percent-encoded.

The href attribute specifies a URL, and URLs must follow specific syntax rules defined by RFC 3986. Spaces and some other characters are considered illegal in URLs. To include a space in the URL, use the percent escape sequence %20 in place of the space character.

Incorrect example with an illegal space in the query string:

<a href="search.html?q=my search">Search for 'my search'</a>

Correct example using percent-encoding for the space:

<a href="search.html?q=my%20search">Search for 'my search'</a>

Replace all spaces in URLs within href attributes with %20 to ensure W3C validation and proper browser behavior.