To allow easir adaptation of data already serialized as JSON, HCL native syntax allows both equals signs _and_ colons for object constructors. This was already implemented, but not reflected in the pseudo-BNF in the specification.
This changed during development as we iterated on the prototype, but the spec is lagging behind.
The main HCL package is more visible this way, and so it's easier than having to pick it out from dozens of other package directories.
Martin Atkins