Merge Strategy 'first|unique|hash' documentation is unclear

The documentation for the [`first|unique|hash`](https://puppet.com/docs/puppet/5.3/hiera_merging.html#strategy--firstuniquehash) merge strategy is brief, and does not explain usage or functionality of the merge strategy in a similar way to the documentation for the other merge strategies.

The entirety of the current documentation for this strategy is one sentance:

> Same as the string versions of these merge behaviors.

This doesn't tell me anything, since obviously it's not the same, or it wouldn't be an additonal option. Mainly, I believe it's implying that hiera will try to select the appropriate strategy based on the data-type. However that raises the question of how the `unique` or `hash` strategy would be applied to a key when `first` is also present (which ignores all merge's entirely).