REST API Search query documentation?

The REST API has a set of search endpoints, but no documentation on what goes in the Filter and Query fields:

Query string Query is not required but you should use either Query or Filters otherwise you'll get all documents in the search index. Optional
Filters string Filters is not required but you should use either Query or Filters otherwise you'll get all documents in the search index. Optional

Where can I find documentation and/or examples of using this?

Thanks, Clyde

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