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>Related W3C validator issues
An end tag </code> has been found violating nesting rules. Check other errors in the same document related to the <code> element, and fix the unallowed nested elements.
End tag “i” violates nesting rules because the closing </i> does not match the most recently opened still-unclosed inline element, causing mis-nested tags.
HTML requires elements to be properly nested in a stack-like order: last opened, first closed. Inline elements like the i element (for idiomatic text), em, strong, a, and span must not overlap. When you open i and then open b, you must close b before closing i. Mis-nesting often happens around links or emphasis tags, e.g., i inside a but closed outside. The i element is purely presentational/idiomatic; consider em for emphasis or CSS with font-style: italic;, but whichever you use, keep the nesting consistent.
Common patterns that trigger the error:
- Overlapping inline elements: i … b … </i> … </b>
- Closing order mismatch across a, span, em, strong, i
- Copy/paste around icons or screen-reader text
Fix by reordering the tags so they close in reverse order of opening, or by merging styles into one element to avoid overlaps.
HTML Examples
Incorrect (reproduces the validator error)
<p>
<a href="/about"><i>About <strong>Us</i></strong></a>
</p>Correct (properly nested)
<p>
<a href="/about"><i>About <strong>Us</strong></i></a>
</p>An <a> tag 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>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.
Spaces are not permitted in the href value for phone links; the phone number must be a continuous string without spaces or slashes.
The href attribute of an anchor (<a>) element defines the link’s destination. For phone numbers, the proper URI scheme is tel:, not callto:. According to the HTML standard and the WHATWG Living Standard, the phone number should contain only digits and may use plus (+) or hyphen (-) characters for formatting, but it should not include spaces or slashes.
Incorrect HTML:
<a href="callto:07142/ 12 34 5">Call us</a>Correct HTML:
<a href="tel:0714212345">Call us</a>With country code and optional formatting:
<a href="tel:+49714212345">Call us</a>For best compatibility and validation, always use the tel: scheme and ensure the phone number string contains only allowed characters.