Three distinct frameworks support the EPUB document type:
NCX - A declarative global navigation definition.
OCF - The Open Container Format(OCF) defines a mechanism by which
all components of an Open Publication Structure(OPS) can be combined into a single
OPF: - The Open Packaging Format(OPF) defines the mechanism by
which all components of a published work conforming to the Open Publication Structure(OPS)
standard including metadata, reading order and navigational information are packaged into
an OPS Publication.
Note:Oxygen XML Editor plugin supports both OPF 2.0
and OPF 3.0.