# User-defined serialization attributes

Any number of user-defined attributes may be defined on `xsl:output`. These attributes must have names in a non-null namespace, which must not be either the XSLT or the Saxon namespace. The value of the attribute is inserted into the `Properties` object made available to the `Receiver` handling the output; they will be ignored by the standard output methods, but can supply arbitrary information to a user-defined output method. The name of the property will be the expanded name of the attribute in JAXP format, for example "{http://my-namespace/uri}local-name", and the value will be the value as given in the stylesheet.

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