Functions defined in the XBRL function registry can be called from within an XSLT context for transforming XBRL instance documents. These XBRL functions are defined in one of two namespaces:
http://www.xbrl.org/2008/function/instance (usually used with the xfi: prefix)
http://www.xbrl.org/2010/function/formula (usually used with the xff: prefix)
So the XBRL function xfi:context, for example, expands to http://www.xbrl.org/2008/function/instance:context (assuming this namespace has been bound to the xfi: prefix).
For a complete list of the functions, go to http://www.xbrl.org/functionregistry/functionregistry.xml.
