Saving this class:

data class StdTitle(@field:JacksonXmlProperty(isAttribute = true, namespace = "http://www.w3.org/XML/1998/namespace", localName = "lang") var lang: String = "")

will produce the following XML when namespace repairing is true:

<StdTitle xmlns:wstxns1="http://www.w3.org/XML/1998/namespace" wstxns1:lang="en"/>

However, the xml: prefix and the http://www.w3.org/XML/1998/namespace namespace is implicitly defined on all XMLs and there is no need to generate xmlns for that.