HTML Validation

Attribute “xmlns:v” not allowed here.

About This HTML Issue

The xmlns:v attribute is not valid on the html element in HTML5.

HTML5 does not support custom XML namespaces like xmlns:v, which was used in old versions of Internet Explorer for VML (Vector Markup Language). The xmlns:v attribute is unnecessary and should be removed to make your HTML valid.

Example before (invalid HTML):

<!DOCTYPE html>
<html xmlns:v="urn:schemas-microsoft-com:vml">
  <head>
    <title>VML Example</title>
  </head>
  <body>
<!-- content -->

  </body>
</html>

Example after (valid HTML):

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>VML Example</title>
  </head>
  <body>
<!-- content -->

  </body>
</html>

For vector graphics in modern HTML, use the svg element instead of legacy VML.

Last reviewed: May 12, 2025

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Related W3C Validator Issues

Attribute with the local name “xmlns:serif” is not serializable as XML 1.0

Bad value “https://www.w3.org/1999/xlink” for the attribute “xmlns:link” (only “http://www.w3.org/1999/xlink” permitted here).

Attribute with the local name “xmlns:svg” is not serializable as XML 1.0.

Remove the xmlns:svg attribute from the <svg> element, leaving only the valid xmlns attribute.

The xmlns attribute defines the XML namespace for the SVG and is correctly set to http://www.w3.org/2000/svg. The xmlns:svg attribute attempts to declare a prefixed namespace, which is unnecessary and invalid in both HTML and SVG served as XML (or embedded in HTML). The W3C validator flags this because HTML5 does not allow arbitrary XML namespace declarations beyond the standard SVG namespace; such prefixes are not used in HTML serialization.

Incorrect usage:

<svg xmlns="http://www.w3.org/2000/svg" xmlns:svg="http://www.w3.org/2000/svg">
<!-- SVG content -->

</svg>

Correct usage:

<svg xmlns="http://www.w3.org/2000/svg">
<!-- SVG content -->

</svg>

Only xmlns="http://www.w3.org/2000/svg" is required for inline SVG in HTML.

Attribute “xmlns:serif” not allowed here.

Bad value “” for the attribute “xmlns” (only “http://www.w3.org/2000/svg” permitted here).

Ensure the xmlns attribute for <svg> elements is set to “http://www.w3.org/2000/svg”.

In HTML documents, the xmlns attribute in an <svg> element must be defined correctly. The xmlns attribute specifies the XML namespace for an SVG element, which should always be “http://www.w3.org/2000/svg”. If you receive a validation error indicating a bad value for xmlns, it means that the attribute is empty or incorrectly set. This namespace ensures that the SVG elements are properly recognized as SVGs by the browser and aids in maintaining proper structure and function.

Here’s a correct example of an <svg> element:

<!DOCTYPE html>
<html lang="en">
  <body>
    <svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
      <circle cx="50" cy="50" r="40" stroke="black" stroke-width="3" fill="red" />
    </svg>
  </body>
</html>

Ensure that every <svg> element you use includes the xmlns attribute with the correct value to avoid validation issues and ensure complete browser compatibility.

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