Feature request: add a way to "tag" fields/groups from base classes to be shown in the docs of derived classes

[woutdenolf]

Many application definitions copy&paste fields/groups with docs-strings from base classes because they are very relevant to the application definitions and it needs the be clear at first glance. We have links to click on but this leads to the full doc of the base class without a way to clarity which fields of the base class are relevant.

NXstress is a recent base class that has several of these:

Originally posted by @PeterC-DLS in #1039 (comment)

The request is to add a feature in the XML syntax to "tag" fields of base classes so that get rendered in the derived class (usually an application definition).

[mkuehbach]

Include also for application definitions thus enabling automated generation of class grouping parts of the documentation see related thoughts and proposal for manual grouping here #1428