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Mike Kelly, the author of the HAL specification, comments that omitting additional metadata in the HAL specification was "intentional" in order to keep it "focused on linking". However, he also suggests that "HAL is therefore a good candidate for use as a base media type on which to build more complex capabilities". This has spurred developers of RESTful APIs to shore up this gap through alternative hypermedia types (such as api+json, collection+json, hyper+json, and siren+json). Unfortunately, none of them have the maturity and broad acceptance that HAL does. Also, some of them require too many complexity complex in order to add simple hypermedia to the resource. HAL, on the other hand, is relatively lightweight and easy to implement and consume.
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