[1] Mozilla XForms Specials - Archive of obsolete content | MDN (2014-04-15 00:00:08 +09:00 版) https://developer.mozilla.org/en-US/docs/Archive/Web/XForms/Mozilla_XForms_Specials

In the XForms 1.0 specification there is no way to get to the instance element from an instance data node. We have added a function via the getFeature() call on each node, that allows the form author to do that. That is, if instanceNode is a node in an instance document, then:
instanceNode.getFeature("org.mozilla.xforms.instanceOwner", "1.0")
will return the <instance> element (in the main document) that the node belongs to.