Inheritance from the NXobject base class

[rayosborn]

It was decided at the last NIAC meeting in September that the NXobject base class should be used to define objects that are valid in all other base classes. This needs to be implemented by adding the appropriate classes to the NXobject NXDL file.

According to the documentation, I believe that the following classes should be added: NXcollection, NXdata, NXgeometry, NXlog, NXnote, NXparameters, NXtransformations.

I believe it also makes sense to add the partial name patterns that have reserved suffixes, so that these can also be validated in any base class: GROUPNAME_log, FIELDNAME_set, FIELDNAME_errors, FIELDNAME_weights, FIELDNAME_mask.

I will submit a PR to implement this policy.

[phyy-nx]

For reference, specific NIAC vote was here:
#1442 (comment)

[prjemian]

The NXobject class was introduced to be the parent of all other classes. I agree that NXroot is exceptional since it never falls under NXentry. I amend as follows:

The NXobject class is the parent class of all classes except NXroot.

Further: It is intended that NXobject never be assigned to a NX_class="NXobject" attribute in a NeXus file.

[prjemian]

As I recall, the NXroot class was introduced as a place where common file-level attributes could be provided with standardized names. Oldest to newest, these are relevant issues and PRs (which are closed at this time):

• add attribute NX_class="NXroot" to NXroot NXDL #149
• /NXroot/@HDF5_Version attribute spelling inconsistent with NAPI #189
• Attribute descriptions for NXroot #466
• NXroot - Wrong type for @file_time and @file_update_time #783
• NXroot. Use NX_DATE_TIME and not NX_CHAR #784
• Missing @creator_version in NXroot #789
• NXroot attributes and a word of caution #836