.. auto-generated by script ../../../../utils/nxdl2rst.py from the NXDL source NXroot.nxdl.xml

.. index::
    ! NXroot (base class)
    ! root (base class)
    see: root (base class); NXroot

.. _NXroot:

======
NXroot
======

**Status**:

  base class, extends :ref:`NXobject`

**Description**:

  Definition of the root NeXus group.

**Symbols**:

  No symbol table

**Groups cited**:
  :ref:`NXentry`

.. index:: NXentry (base class); used in base class

**Structure**:

  .. index:: NX_class (file attribute)

  **@NX_class**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    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.

    Obligatory value:  ``NXroot``

  .. index:: file_time (file attribute)

  **@file_time**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    Date and time file was originally created

  .. index:: file_name (file attribute)

  **@file_name**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    File name of original NeXus file

  .. index:: file_update_time (file attribute)

  **@file_update_time**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    Date and time of last file change at close

  .. index:: NeXus_version (file attribute)

  **@NeXus_version**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    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.

  .. index:: HDF_version (file attribute)

  **@HDF_version**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    Version of HDF (version 4) library used in writing the file

  .. index:: HDF5_Version (file attribute)

  **@HDF5_Version**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    Version of HDF5 library used in writing the file.

    Note this attribute is spelled with uppercase "V",
    different than other version attributes.

  .. index:: XML_version (file attribute)

  **@XML_version**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    Version of XML support library used in writing the XML file

  .. index:: h5py_version (file attribute)

  **@h5py_version**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    Version of h5py Python package used in writing the file

  .. index:: creator (file attribute)

  **@creator**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    facility or program where file originated

  .. index:: default (file attribute)

  **@default**: (optional) :ref:`NX_CHAR <NX_CHAR>`

    .. 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.

  **(entry)**: (optional) :ref:`NXentry`

    entries

**NXDL Source**:
  https://github.com/nexusformat/definitions/blob/master/base_classes/NXroot.nxdl.xml