An unvalidated set of terms, such as the description of a beam line. Use :ref:`NXcollection` to gather together any set of terms. The original suggestion is to use this as a container class for the description of a beamline. For NeXus validation, :ref:`NXcollection` will always generate a warning since it is always an optional group. Anything (groups, fields, or attributes) placed in an :ref:`NXcollection` group will not be validated.