Tagging & filtering of example fields by characteristics & contexts

General feature idea

(As identified during a video call discussion yesterday with @davidhassell.) We now have 12 example fields all of which are distinguished by their numbering only, but they can be grouped according to notable characteristics and contexts, not all of which are across contiguous fields under this ordering due to the historical/practical order of addition to the examples, for instance:

• DSG feature fields: 3, 4, 11;
• UGRID mesh topologies: 8-10;
• time series: 3, 4, 6;

etc. Whilst the documentation is good in that we have a table which provides a brief description of each numbered field which often mentions these, we agreed it would be useful to have a means to tag the fields with keywords describing such shared characteristics and contexts (and perhaps more e.g. for ones which have certain constructs such as cell methods) and, ideally, on top of this provide some means to filter on such keywords and on general metadata properties of the fields too.

Start by reviewing the documentation table for the 12 numbered example fields and the current handling of field metadata. Define the desired tags and filtering behavior for shared characteristics, contexts, and general metadata properties; done requires an agreed design and an implemented way to apply and filter those tags.