XML Skeleton files are very similar to MillScript XML templates, except they use named, rather than numbered, parameters. They are also written in XML augmented with some custom tags.
There are only three differences between an XML skeleton and an XHTML skeleton:
.xml.sk. e.g.
myXmlSkeleton.xml.sk
<field name="body" xmlns="http://www.millscript.org/namespace/skeleton" />
<xml xmlns:sk="http://www.millscript.org/namespace/skeleton">
<hotels>
<hotel>
<name><sk:field name="name">The parameter with name "name" is the hotel name</sk:field></name>
</hotel>
</hotels>
</xml>