Syntaxt of selection is located at
https://pkg.go.dev/github.com/ipld/go-ipld-selector-text-lite#SelectorSpecFromPath

Example use, assuming that:
  - The root of the deal is a plain dag-pb unixfs directory
  - The directory is not sharded
  - The user wants to retrieve the first entry in that directory

  lotus client retrieve --miner f0XXXXX --datamodel-path-selector 'Links/0/Hash' bafyROOTCID ~/output

For a much more elaborate example see the top of ./itests/deals_partial_retrieval_test.go

…retrieval

…ctor-retrieval