The iXML library is meanwhile available in all 4.6C basis and application development systems.
Originally the iXML classes and interface had only been available as local ones. In the meantime global classes and interface are available, which allow you to pass interface references to function modules etc.
In order to enable the iXML library, you have to add the following two lines to your code:
type-pools: ixml.
class cl_ixml definition load.