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

Namespace declarations like xmlns:dc on an <svg> element are not serializable as XML 1.0 when used in an HTML5 document.

In HTML5 (the text/html serialization), namespace declarations using the xmlns: prefix syntax are not valid attributes. The HTML parser does not treat these as actual XML namespace declarations — it sees them as regular attributes with a colon in the name, which cannot be serialized back to well-formed XML 1.0. This commonly happens when SVG code is exported from graphic editors like Inkscape or Adobe Illustrator, which include Dublin Core (dc), RDF, and other XML namespace declarations that are unnecessary for rendering.

The SVG will render perfectly fine in browsers without these namespace prefixes. If the <svg> element doesn't actually use any elements or attributes from those namespaces (like <dc:title>), you can safely remove them. If it does contain such elements, those elements are also typically unused by browsers and can be removed as well.

Invalid Example

<svg xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  viewBox="0 0 100 100">
  <metadata>
    <rdf:RDF>
      <rdf:Description rdf:about="">
        <dc:title>My Icon</dc:title>
      </rdf:Description>
    </rdf:RDF>
  </metadata>
  <circle cx="50" cy="50" r="40" fill="blue" />
</svg>

Valid Example

Remove the namespace declarations and any associated metadata elements:

<svg viewBox="0 0 100 100">
  <circle cx="50" cy="50" r="40" fill="blue" />
</svg>

If you still want to provide a title for accessibility, use the standard SVG <title> element instead:

<svg viewBox="0 0 100 100" role="img">
  <title>My Icon</title>
  <circle cx="50" cy="50" r="40" fill="blue" />
</svg>

Learn more:

MDN Reference

HTML Namespaces - MDN Web Docs

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WHATWG Spec

XHTML and XML Serialization

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