YAML as a JSON superset and TAB characters

Question

I am unable to find a reference to this error exactly, but YAML 1.2 says it\'s a JSON superset, and if I use tab characters in a JSON it treats it like an error.

e.g.

Answer 1

I know why YAML historically disallows tabs, but how can I interpret this in the context of JSON-superset?

Taking the rest of the specifications into account, we can only conclude that the "superset" comment is inaccurate. The YAML specification is fundamentally inconsistent in the Relation to JSON section:

YAML can therefore be viewed as a natural superset of JSON, offering improved human readability and a more complete information model. This is also the case in practice; every JSON file is also a valid YAML file. This makes it easy to migrate from JSON to YAML if/when the additional features are required.

JSON's RFC4627 requires that mappings keys merely “SHOULD” be unique, while YAML insists they “MUST” be. Technically, YAML therefore complies with the JSON spec, choosing to treat duplicates as an error. In practice, since JSON is silent on the semantics of such duplicates, the only portable JSON files are those with unique keys, which are therefore valid YAML files.

Despite asserting YAML as a "natural superset of JSON" and stating that "every JSON file is also a valid YAML file", the spec immediately notes some differences regarding key uniqueness. Arguably, the spec should also note the differences around using tabs for indentation here as well.

Speaking of which, as the validator implied, YAML explicitly prohibits tabs as indentation characters:

To maintain portability, tab characters must not be used in indentation, since different systems treat tabs differently. Note that most modern editors may be configured so that pressing the tab key results in the insertion of an appropriate number of spaces.

This is, of course, stricter than the JSON specification, which simply states:

Whitespace can be inserted between any pair of tokens.

So, to directly answer your questions...

(e.g. Is YAML not an actual superset or does JSON also disallow tabs? Or the spec does allow for tabs in this case but the implementation is not there yet?)

...YAML is not actually a superset, JSON does not disallow tabs, whereas the YAML specification does indeed disallow tabs explicitly.