Attribute is repeated

What it means

An element may not carry the same attribute name twice. Unlike HTML, where a browser silently keeps the first, XML treats it as a well-formedness error and refuses the document.

In namespaced documents the rule applies after prefix resolution, so two different prefixes bound to the same URI count as a duplicate even though the text differs.

What usually causes it

• A merge that applied the same attribute from two sources.
• A template that adds a default attribute and then adds it again conditionally.
• Two prefixes bound to one namespace URI, colliding after resolution.
• Hand-editing that duplicated an attribute rather than replacing it.

How to fix it

• Remove the duplicate; decide deliberately which value wins.
• Build attributes in a map keyed by expanded name so collisions are impossible.
• Check for two prefixes bound to the same namespace URI.

The same error elsewhere

Different parsers, same defect. If you arrived with one of these messages, you are in the right place.

• Xerces (Java)

  Attribute "href" was already specified for element "link".

• libxml2 (PHP, lxml, Nokogiri)

  Attribute href redefined

• expat (Python)

  duplicate attribute: line 1, column 30

• .NET System.Xml

  'href' is a duplicate attribute name.