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# Attribute “xmlns:w” not allowed here. > Canonical HTML version: https://rocketvalidator.com/html-validation/attribute-xmlns-w-not-allowed-here > Attribution: Rocket Validator (https://rocketvalidator.com) > License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) In HTML5, the only namespace-related attribute permitted on the `` element is `xmlns` with the value `http://www.w3.org/1999/xhtml`, and even that is optional—it exists solely for compatibility with XHTML serialization. Prefixed namespace declarations like `xmlns:w`, `xmlns:o`, `xmlns:v`, and similar attributes are XML features that have no meaning in the HTML syntax. They originate from Microsoft Office's HTML export, which generates markup containing proprietary XML namespaces such as `urn:schemas-microsoft-com:office:word` for Word-specific elements and styling. ## Why This Is a Problem **Standards compliance:** The HTML living standard (WHATWG) explicitly does not support custom namespace declarations. Including them makes your document non-conforming, and the W3C validator will report an error for each one. **No browser benefit:** Modern browsers parsing HTML5 ignore these namespace declarations entirely. The attributes serve no functional purpose on the web—they only add unnecessary bloat to your markup. **Maintenance and readability:** Office-generated HTML is notoriously verbose. Leaving namespace declarations in place often goes hand-in-hand with other Office artifacts (conditional comments, `` tags, `mso-` style properties) that clutter your code and make it harder to maintain. **Accessibility and interoperability:** While browsers typically tolerate these extra attributes without visible issues, non-browser HTML consumers—such as screen readers, search engine crawlers, or email clients—may handle unexpected attributes unpredictably. ## How to Fix It 1. **Remove the `xmlns:w` attribute** from your `` tag or any other element where it appears. 2. **Remove related namespace declarations** like `xmlns:o` (Office), `xmlns:v` (VML), and `xmlns:m` (Math) if present. 3. **Clean up Office-specific elements** such as ``, ``, or `` that depend on those namespaces—these are not valid HTML elements. 4. **Strip Office-specific CSS** properties prefixed with `mso-` (e.g., `mso-bidi-font-family`) that often accompany namespace declarations. If you regularly paste content from Microsoft Word, consider using a "paste as plain text" feature in your editor, or use an HTML cleaning tool to strip Office artifacts automatically. ## Examples ### Invalid: Office namespace on the `` element ```html Document

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``` ### Invalid: Multiple Office namespaces ```html Document

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``` ### Valid: Clean HTML without namespace declarations ```html Document

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``` ### Valid: Using the standard `xmlns` attribute (optional) If you need XHTML compatibility, the standard `xmlns` attribute (without a prefix) is permitted: ```html Document

Content from Word

``` Note that this same validation error applies to any custom prefixed namespace attribute—not just `xmlns:w`. If you see similar errors for `xmlns:o`, `xmlns:v`, `xmlns:st1`, or others, the fix is the same: remove them along with any elements or attributes that depend on those namespaces.