CII
CII (Cross Industry Invoice) is a UN/CEFACT XML syntax for invoices, one of the two ways an EN 16931 invoice can be expressed.
CII is the syntax used inside ZUGFeRD and Factur-X files. Like UBL, it maps the same EN 16931 data model, just with a different set of XML tags.
Because ZUGFeRD is so common in Germany, CII shows up on a large share of German e-invoices even though the person handling them may never see the XML.
Cortena reads CII data from hybrid and structured invoices as part of normal intake.