Unstructured data save should add UGRID to the file conventions

[pp-mo]

Though N.B. I believe there is still some room for doubt about what the exact result should look like.

see Netcdf User Guide Appendix A, under "conventions" :

"""It is possible for a netCDF file to adhere to more than one set of conventions, even when there is no inheritance relationship among the conventions. In this case, the value of the 'Conventions' attribute may be a single text string containing a list of the convention names separated by blank space (recommended) or commas (if a convention name contains blanks). """

So, whether "UGRID 1.0" replaces "CF 1.7", or adds to it, or whatever, not quite sure as yet.
UGRID sample files that I have seen all say just "UGRID 1.0",
( like this example in the UGRID repo )
but that will of course upset the cf-checker, since the 'adoption' relationship between the two is not yet formally agreed(as-of Oct 2022).

[pp-mo]

Update
CF refers to netCDF docs @4.9, which does make a statement here
( see "Conventions" in here )

It is possible for a netCDF file to adhere to more than one set of conventions, even when there is no inheritance relationship among the conventions. In this case, the value of the 'Conventions' attribute may be a single text string containing a list of the convention names separated by blank space (recommended) or commas (if a convention name contains blanks).