XML element referencing

Is it possible that an XML file for tree can have an element refereces another element? Also, if not then how can we acheive this?

E.g. <?xml version="1.0" encoding="iso-8859-1" ?>

<item text = “CENTRAL2” reference="region_CENTRAL">

When loading data from XML - the parent-child relation can be defined only by tag nesting.
It doesn’t possible to define relation in any other way.