Definition of the root NeXus group. The root of any NeXus data file is an ``NXroot`` class (no other choice is allowed for a valid NeXus data file). This attribute cements that definition. Date and time file was originally created File name of original NeXus file Date and time of last file change at close Version of NeXus API used in writing the file. Only used when the NAPI has written the file. Note that this is different from the version of the base class or application definition version number. Version of HDF (version 4) library used in writing the file Version of HDF5 library used in writing the file. Note this attribute is spelled with uppercase "V", different than other version attributes. Version of XML support library used in writing the XML file Version of h5py Python package used in writing the file facility or program where file originated entries .. index:: plotting Declares which :ref:`NXentry` group contains the data to be shown by default. It is needed to resolve ambiguity when more than one :ref:`NXentry` group exists. The value is the name of the default :ref:`NXentry` group. It is recommended (as of NIAC2014) to use this attribute to help define the path to the default dataset to be plotted. See http://wiki.nexusformat.org/2014_How_to_find_default_data for a summary of the discussion.