concatenating files

I'm not sure if this should go here or to the main fsspec repo.

I'd like to use the reference filesystem to concatenate pieces. That is, for one reference, I'd like to specify a list of things to join together for making up a new file in stead of just having a single pointer. This could roughly look like:

"refs": {
      "key0": ["data", ["http://target_url", 10000, 100]],
      "key1": [["http://target_url", 10000, 100], ["http://{{u}}", 10000, 100]],
    }

etc... Using that method, one could completely rearrange existing files.
In my current application, I'd like to join existing chunks of uncompressed netCDF file into a single larger chunk to be used within zarr.

A potential issue might be, that the following would become ambiguous:

"refs": {
      "key0": ["https://test"],
    }

This could refer to either just a single piece of raw data containing the text "https://test" or a reference to the entire object behind the link. However, it should be possible to disambiguate this, by defining that single-element raw data blocks must always be written without the list.

Start by reviewing the reference filesystem and the existing reference format handling described in this issue. Trace how a reference currently resolves a single pointer, then determine how concatenated pieces and the single-element ambiguity should be represented. Done means the format and behavior are specified well enough to support rearranging referenced data, including the netCDF-to-zarr use case.